550 PROCEEDINGS OF THE ACADEMY OE 



Two specimens were exhibited ; one, a skin brought from the Ogobai River, 

 "Western Africa, by Mr. P. B. Du Chaillu ; the other, the skull of a half-grown 

 individual, obtained from the Museum of the Pennsylvania University. These 

 jMr. Cope regarded as belonging to a species hitherto unknown, and which he 

 proposed calling Osteolaemus tetraspis. He briefly characterized it as fol- 

 lows : Proportions of the head somewhat similar to those of Crocodilus 

 trigonops, Gray, of India. Breadth of muzzle at ninth tooth equal to the 

 distance between the external nasal orifice and anterior border of the orbit, and 

 to the width of the table of the cranium posteriorly. A short ridge in front of 



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 each orbit, directed obliquely inward. Teeth , rather compressed. Four 



15 

 nuchal shields, in a single transverse series ; four cervical, in pairs. Dorsal 

 shields in sir rows. Posterior extremities without fringe. Total length of 

 the entire specimen, five feet. 



Mr. Cope alluded to the remarkable extent to which ossification was carried 

 in this species. The cranium was much more rugose and pitted than in the 

 adult, specimens of much larger species, and the crotaphite foramina were roofed 

 over by bone. The latter peculiarity was sometimes observed in the genera 

 Jacare and Caiman. The osseous gular and thoracic buckler was also similar 

 to that exhibited by those genera, and by the extinct "Crocodilus" Hast- 

 ing s i ae , the existence of which has been shown by Professor Huxley. And 

 alluding to the numerous points of analogy to the Alligatorial or American type, 

 Mr. Cope mentioned the occurrence of South American forms of tree-snakes 

 in Western Africa; e. g. Dryophis Kirt 1 a n di i andThrasops f 1 a vigulari s. 

 Ilallowell. 



Mecistops bathyrhynchus was the name by which Mr. Cope proposed to 

 characterize a species, of which a large skull was in the Academy's museum. 

 This skull was of a very elongate form ; on this account, and from the fact that 

 the nasal bones disappeared some distance posterior to the external nasal ori- 

 fice, he concluded that it belonged to Mecistops, Gray, although that genus 

 was mainly characterized by the position of the cervical dermal shields. 

 The breadth of the muzzle at the tenth tooth was twice that at. the notch, and 

 was contained two and half times in the space between the orbit and nasal ori- 

 fice. The length of the muzzle anterior to the tenth tooth equalled the length 

 posterior to that point, plus three-fourths the length of the orbit. The latter 

 was scarcely larger than the external nasal orifice. The width of the table of 

 the cranium posteriorly, entered into the total length, measured from the pos- 

 terior border of the former, four times; was equal to the length of the symphy- 

 sis mandibuli ; was greater than the width of the muzzle measured across the 

 palate between the twelfth and thirteenth teeth, and was exactly twice the width 

 of the os frontis. The snout was more rounded and elevated than in the known 

 species of Mecistops ; the superiormaxillaryboneatitsposteriorextremity formed 

 a perpendicular wall. The length of the ramus of the inferior maxillary from 

 the angle, was thirty-two inches, the symphysis extending one-fifth the distance. 



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 Neither ridge nor convexity in front of the orbits Teeth . Native country 



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 of the species unknown. 



Mr. Cope stated that in the present species the muzzle was less depressed, 

 and more rounded laterally than in the species of Crocodilus; also that the 

 fourth and tenth teeth above, and fourth below, were of proportionally large size. 



Mr. Lea read two letters from Prof. Tyson, State Geologist of Maryland, in 

 relation to some remarkable infusorial beds of Tripoli, observed by him in 

 Maryland. The specimens were presented to the Academy: 



No. 1 is from a bluff on the Patuxent, below Lyon's Creek, the bed being 

 three feet thick, overlying the green sand. 



No. 2 is from a bluff two miles below Nottingham, the thickness ten feet. 



[Dee. 



