68 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



base of ventral fin, 10.* The dorsal and ventrjjl scuta correspond in 

 number to the vertebrse. 



Measurements. 



M. 



Length of portion of fish preserved 0. 121 



Length of head 0.030 



Width of head behind 0, 008 



Depth of body at end of pectoral fin 0.0035 



Depth of body behind ventral fin 0. 0070 



Depth of dorsal fin 0.0070 



Length of dorsal fin 0. 0040 



This fish was discovered by Dr. F. V. Hayden, Geologist-in-Charge of 

 the United States Geological Survey of the Territories in the Niobrara 

 Cretaceous horizon of Dakota. 



Leptoteachelus longipinnis, sp. nov. 



This species agrees with the type-species of Leptotrachelus of Yon der 

 Marck in the position of the ventral fins beneath the dorsal, in the 

 great elongation of the anterior vertebrse, and in the lanceolate form of 

 the head. It differs from that species {L. armatus v. d. Marck) in its 

 more elongate dorsal fin, in which it approximates the genus Dercetis. 



Two incomplete specimens represent this species, neither of which 

 possesses the caudal nor exhibits an anal fin. In one of them, the cra- 

 nium is preserved in a somewhat dislocated condition at the extremity 

 of its very long peduncle. The vertebrae of this region, which might 

 be called a neck, are several times as long as those of the dorsal series. 

 The femoral bones are slender, and commence below the anterior part of 

 the dorsal fin. In one specimen, the ventral fin originates below the 

 twelfth dorsal ray; in the other, below the fifth. As the latter is the 

 least distorted, I suspect the fin to occupy its normal position. The 

 dorsal radii are slender, and the middle and anterior longer than the 

 posterior; they number twenty-seven in one specimen, and nineteen in 

 the other, where the posterior portion is broken away. The ventral 

 rays are hair-like, and do not extend to the line of the distal end of the 

 dorsal. The pectoral fins are well developed, and occupy their usual 

 position. The cranium is much dislocated, but the snout is acute and 

 attenuated. The dermal scuta consist of median, dorsal, and ventral 

 rows of tripodal form. There are some slender, longitudinal, hair-like 

 bodies on the sides, which cross the ribs. The vertebrse present the 

 characteristic elongate centra. The diapophyses are longer on the post- 

 ventral than on the preventral region. Each scutum is as long as a ver- 

 tebra. 



Measurements. 



M. 



Length of neck of No. 1 0.045 



Length of neck to base of dorsal fin 0. 071 



Length of base of dorsal fin 0. 025 



Elevation of dorsal fin 0.009 



