141 



of the jaw, corresponding to the situation of Professor Owen's 

 sketch of the premolar, Dr. Jackson had made a large and deep 

 excavation, exposing the fangs of the second tooth, removing 

 some of the bone from between them, and opening freely into 

 the dental canal, but without finding any appearance of the 

 tooth which Professor Owen considers as characteristic of the 

 Mastodon. Dr. Hays, also, in his paper upon the " Inferior 

 Maxillary Bones of Mastodons," &c., (Transactions of the Ame- 

 rican Philosophical Society, Vol. IV. p. 319,) speaks of having 

 examined about forty lower jaws, but says nothing of such a 

 tooth. 



Dr. Jackson then alluded, for explanation, to that part of his 

 former Report upon the Cambridge Collection, (Proceedings of 

 the Society, October, 1845,) in which he speaks of six as the 

 true number of the molar teeth in 31. giganteum, at least in the 

 lower jaw, and in which he inferred, from a statement of Pro- 

 fessor Owen, (Annals of Natural History, Vol. XI. p. 330,) 

 that he considered five as the number ; the inference was cer- 

 tainly a fair one. He now finds that in the Odontography, 

 which he had not seen when his Report was made. Professor 

 Owen describes seven molars, generally so called, on each side 

 and in each jaw, but with the saving clause above quoted in 

 regard to the lower. Dr. Jackson's observation, then, as to the 

 number of the molar teeth in the lower jaw, corresponds with 

 that of Professor Owen, except for the " small premolar," of 

 the existence of which no proof has yet been given. 



Dr. Gould announced that, being employed in the exam- 

 ination of the Shells collected by the United States Explor- 

 ing Expedition, commanded by Charles Wilkes, U. S. N., 

 he proposed to read before the Society, from time to time, 

 as they might be prepared, descriptions of the new species, 

 in anticipation of their future publication, in a more ex- 

 tended form, and fully illustrated by figures, as one of the 

 volumes of the great work on the Expedition, issued by 

 Congress. 



He commenced with the following species of the genus 

 Chiton. 



