100 PROCEEDINGS OF THE ACADEMY OF 



Prof. Lkidy, exhibited the fragment of a jaw of a Crocodile, recently sent 

 to him for examination by Prof. F. V. Hayden, now engaged in geological ex- 

 ploration of part of our western territories. The specimen, together with a 

 multitude of small fragments of bones, scales, and teeth of ganoid and other 

 fishes, was found at the junction of the Big Sandy and Green River. 



The fragment from the fore part of the jaw indicates an animal about the 

 size of the Alligator of the Mississippi, and apparently a head of nearly the 

 same form. The external surface of the jaw is exceedingly rough and pitted. 

 Two entire teeth, and the remains of two others are retained in the specimen. 

 The larger of the perfect teeth, apparently, holding the position correspond- 

 ing with a canine, has a blunt conical crown strongly carinated fore and aft, 

 and with the enamel finely rugose. The length of the crown is 8 lines; its diame- 

 ter antero-posteriorly 7 lines ; and transversely 6^ lines. The specimen per- 

 tains to an extinct species, probably different from any heretofore indicated. 

 The character of the formation from which it was obtained and its geological 

 age I have not learned. 



I propose to dedicate the species to Mr. Henry W. Elliott, a young and able 

 artist, attendant on Prof. Hayden's expedition, with the name of Crocodilus 

 Elliotti. 



Prof. Leidy stated that during the last summer he had made some further 

 observations on Urnatella, a genus of ciliated polyps of the family Pedicelli- 

 nidae, discovered by him some years ago (Pr. Ac. Nat. Sc. 1851, 321; 1854, 191) 

 in the Schuylkill River. It is found abundantly below the dam at Fairmount, 

 adhering to stones and rocks, on the sides and under part not in contact with 

 the ground. Occasionally it is observed attached to the shell of the living 

 JJnio complanatus, and Melania virgi?iica, and less frequently to the stem of 

 Schollera graminea and the leaves of Vallisneria spiralis. In the locality named, 

 on the rocks, there may be observed, in association with Urnatella, the follow- 

 ing animals : Spongilla fragilis ; Limnias ccratophylli, usually abundant and in 

 compound bunches; Cotharnia pusilla, parasitic on Urnatella and Limnias; 

 Hydra carnea, Ag., Paludicella elongata, Plumatella vesicularis : and the worm 

 Manayunkia speciosa, etc. 



Unlike the marine genera of Pedicellinidas, the polyp stocks of Urnatella 

 are erect or semi-erect, and not prostrate or creeping attached along the sur- 

 face of bodies. Urnatella starts by a thin membranous disk or expansion 

 tightly adherent to the point of support. Usually two stems or stocks (occa- 

 sionally three or only one,) start from the same disk, and diverge from each 

 other in a gentle curve. The stems may be seen from a simple pedicle with- 

 out division, to a series of eleven divisions or segments, exclusive of the 

 polyp head. A colony of Urnatella recalls to mind a miniature patch of 

 plants in a flower garden. The smallest polyps are translucent whitish or 

 nearly colorless ; the largest are less than two lines long, and alternately 

 white and blackish or brownish. When disturbed the polyps retract their 

 arms, hang their heads, and bend downward, so that the heads touch the basis 

 of support, or the stems even become somewhat involute. Voluntarily the 

 polyps are often observed abruptly to move from one side to the other in the 

 most singular manner, as if wearied of remaining too long in the same posi- 

 tion. In these movements the stems bend the entire length, but there is no 

 contraction or shortening. In attempting to detach a polyp, the heads sud- 

 denly bend downward in such a manner as if the violence elicited a feeling of 

 pain in the animal. 



The terminal two or three segments of the parent stems usually give off a 

 branch on each side, and this branch sometimes gives off a second. The 

 branches always consist of a pedicle or single joint supporting a polyp head. 



In a polyp stock of more than two divisions, independent of the polyp head, 

 the additional segments are urn shaped. The penultimate segment is barrel 

 shaped ; the last one cylindrical, or clavatc. 



The polyp heads are provided with from a dozen to sixteen ciliated arms. 



[Sept. 



