382 Scientific Proceedings of the 
Dr. W. also made some remarks upon a skeleton of the sloth (Brady- 
pus tridactylus) prepared by himself. The following are some of the pe- 
culiarities in its structure, viz. its three toes; its walking upon the side 
of the foot; the divergence of the posterior extremities from the pelvis ; 
the articulation of the fibula as well as of the tibia with the astragalus; 
the length of the anterior extremities, so that the fore arm, as well as the 
hand, is planted upon the ground in walking, so as to bring the body into 
a horizontal position; the extensive codssification which takes place in all 
the bones of the hand and foot; the peculiar lateral disposition of the 
claws, and the source of the deception in President Jefferson’s notions of 
the Megalonyx, so philosophically and decisively controverted by Cuvier ; 
the bifurcation of the zygomatic process; and especially the existence of 
nine cervical vertebra instead of seven, as found in all other animals. 
This last point, he observed, was still controverted, it being contended 
that what appears to be a transverse process only, does in fact bear the 
rudiment of arib. Dr. W., however, has been unable to detect any thing 
like an articulating surface in this specimen, an old one, by long macera- 
tion of the bones. The eighth vertebra also has a distinct circular fora- 
men for the vertebral artery, which is the distinctive character of the cer- 
vical vertebra. 
Dr. J. B.S. Jackson remarked, that in regard to the transverse process 
bearing a rudimentary rib, something analogous was found in the human 
foctus, the transverse process of the seventh cervical vertebra being a sep- 
arate piece which afterwards becomes codssified. 
Dr. Srorer stated, that he had received another letter from J. G. AN- 
“tHoNY, Esq., of Cincinnati, communicating the discovery of a new ge- 
nus of the Trilobite family, and that he had submitted it to Mr. Tesche- 
macher ; 
: June 20, 1838.—G. B. Emerson, Esq., President, in the chair. 
Josern P. Cournovuy, Esq., began the reading of a monograph of the 
Family Osteodesmacea of Deshayes, embracing the genera Thracia, Ana- 
tina, Periploma and Osteodesma. He commenced with the genus Thra- 
cia, and shewed the great confusion which now exists in respect to bot 
the generic and specific characters. This had arisen partly from British 
writers having confounded the type of the genus, Anatina declivis, Pen- 
nant, (Anatina myalis, Lam.) with another species, Mya declivis, Donov. 
(Anatina convera, Turton,) and more especially by Blainville supposi™g 
a shell before him to be Anat. myalis, which was not so, but W nat. 
trapezoides, and which he consequently removed from the genus Thracta 
and made it the type of Osteodesma, which genus again, he erroneously 
considers to be synonymous with Periploma, Schumacher. 
originated numerous other mistakes in subsequent writers. 
deavored at great length to reconcile the synonymy of the following spe- 
cies, and the following are the results of his research. 
