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depending solely on age and accidental circumstances of growth. I cannot think, therefore, that there are sufficient reasons for considering the P. procumbens of Hancock as distinct from P. Ehrenbergi.

I have also been unable to find, in the characters assigned by Dr. Leidy* to the species occurring in the neighbourhood of Philadelphia, and named by him Paludicella elongata, sufficient grounds for the separation of the American form as a distinct species from the European one. A slight difference in the length of the cells cannot afford a valid specific difference, and this view is fully borne out by the figure which accompanies Dr. Leidy's paper.

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Genus VII. URNATELLA, Leidy, 1851.

Name.-A diminutive noun, formed from urna, an urn, in allusion to the urn-shaped figure of the articulations.

We find, in the fifth volume of the 'Proceedings of the Academy of Natural Sciences of Philadelphia,' a new Polyzoon described by Dr. Leidy under the name of Urnatella gracilis. It resembles, as Dr. Leidy informs us, a miniature Isis hippuris, and was discovered growing upon the under side of stones, in the River Schuylkill, near Philadelphia. Dr. Leidy accompanies his communication with a figure of the conccium; and though he had not succeeded in detecting the polypides, he felt himself justified in viewing the production in question as a true Polyzoon.

At a subsequent meeting of the Academy (Proc. Acad. Nat. Sc. of Philadelphia,' vol. vii. p. 191), Dr. Leidy again offers some remarks on Urnatella gracilis. Since his previous communication, he had detected the polypides, and had also in other respects succeeded in making a more satisfactory examination of the new Polyzoon, so that he now finds it necessary to alter in some points his previous description.

His account is confined to a generic and specific diagnosis, from which it appears that Urnatella gracilis is a most remarkable animal, and one of the most beautiful of the freshwater Polyzoa. The following are the characters given by Leidy in his amended diagnosis :

Generic character." Conocium consisting of a series of segments up to eighteen in number, and forming free semi-erect curved stems, attached only by the base of the lowest segment. Segments, excepting the three last ones, simple, urniform; the antepenultimate and the penultimate oblong, with simple or compound branches of the same form; the last segment or active polyp is campanulate, and is supplied with cylindrical ciliated arms, arranged in a circle round the mouth." Leidy.

Species unica. Urnatella gracilis, Leidy.

Specific character.-"Stems single or in groups up to six in number, attached at the lower extremity by means of a sienna-coloured granular substance. Urniform segments 225 mm. long by 18 mm. broad, becoming smaller towards the free end of the stems; body portion of each urniform segment translucent, whitish, with sienna-coloured transverse striæ and punctæ, and having on each side near the bottom a roundish process, the remains of former branches; the narrow top and bottom portion of the segments brown in colour and annulated. The antepenultimate and penultimate segments and their branches oblong, translucent. Polyp. 225 to 45 mm. long, campanulate; expanded, mouth circular,

the diameter equal to the length of the body, surrounded by fourteen cylindrical, ciliated, Stems up to 4 mm. in length." Leidy.

retractile arms.

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SYNONYMS.-1854. Urnatella gracilis.

Leidy, Proceedings Acad. Nat. Sci. of Philadelphia, vol. v, p. 321. (Original figure of the cœnocium.) 1854. Urnatella gracilis. vol. vii, p. 191.

Leidy, Proceedings Acad. Nat. Sci. of Philadelphia,

Iconography.-Original figures of the conccium by Leidy.

HABITAT. On the under side of stones in running water.

LOCALITY.-River Schuylkill, in the city of Philadelphia, United States.

Dr. Leidy.

Besides the two short notices contained in the references given above, there is no other published account of this remarkable genus, and zoologists cannot but look forward with impatience to the fuller description promised by its discoverer.

While the present sheets were passing through the press, I received a note from Professor Leidy, along with a pencil sketch of the expanded polypide, from which I have given the accompanying woodcut. "The anatomy of the animal," writes Dr. Leidy, "is easily ex

* From a pencil sketch furnished by Dr. Leidy.

amined, but in numerous specimens I have been unable to detect the slightest trace of generative structures; while on the other hand, the stomach is almost constantly more or less filled with large leucophroid bodies, which I am inclined to suspect are the reproductive bodies."

The annexed figure of Urnatella is so strongly suggestive of the marine genus Pedicellina that I feel much tempted to place Urnatella in the sub-order Pedicellinea, in which it would then become the type of a distinct family in this sub-order. With our present imperfect knowledge of its anatomy, however, such an association would hardly be justified, and I have therefore deemed it most advisable to view it for the present as the type of a sub-order of gymnolæmatous Polyzoa, premising at the same time that this location is to be considered as purely provisional.

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