Cope.] ^'^'^ [Dec. 2, 



broken away, those of the inner row are perfect. The bases of the 

 former are cylindric, the latter are also cylinclric, with conic crowns. 

 Some fragments belonging to this or an allied species i^resent conic prox- 

 imal teeth, while specimens from other collections confirm the reference 

 to Semotilus. 



The expansion of the ala is very gradual, and projects anteriorly rather 

 than outwards. Hence the outer face of the bone is one oblique plane 

 from the bases of the teeth to the edge of the ala. The latter projects 

 beyond the plane of the inner margin, so that the anterior face of the 

 bone is oblique also. The external surface of the ala is cross-ribbed. 

 The j)roximal limb of the bone is contracted, and slightly compressed 

 near the teeth. Teeth 2.5 — ; the interspace between the inner pair, 

 opposite the fourth of the outer series. The bases of the inner descend 

 to the inner anterior margin of the base vertically. 



Measurements. M. 



Length of tooth sei'ies 0.033 



Depth at fourth tooth 019 



" first " Oil 



Width " "■ 0C85 



Length inner tooth Oil 



This chub was larger than the common Eastern species, the S. rhotheus, 

 the largest of the genus. The pharyngeal bone indicates a fish of five 

 or six pounds weight. The gradual and slight expanse of the ala of 

 this bone distinguishes the species from any of the existing ones. Named 

 from the posterior direction of the teeth. 



From St. Catharine's Creek, Idaho ; obtained for Capt Clarence King- 

 by J. C. Schenk Smithsonian, No. 1489. 



Semotilus bairdii. Cope. 



Sp. nov. 



This species differs from the last in the much less expansion of the ex- 

 ternal or alar margin of the pharyngeal bone. It has scarcely any alar 

 prominence of the angle, which also projects so little beyond the inner 

 margin as to render the anterior or perforated surfiice almost transverse. 

 Distal end of the bone gently curved ; proximal limb compressed near tlie 

 teeth. Teeth 3.4 — , those of the inner pair Opposite the third and fourth 

 of the outer series. Bases cylindric ; crowns not preserved ; outer face 

 of the bone with numerous foramina penetrating it backwards. 



Measurements. M. 



Length of tooth series 0.021 



Depth at third tooth 01 



Width " " OOG 



Depth at first " 008 



From the same locality and explorer as the last species. No. 1482. 



This species is dedicated to Prof. Spencer F. Baird, to whom the author 

 is under greater obligations than to any other man, in respect to his 

 special pursuits. 



