1856.] 169 



We had a fine opportunity of studying the genus 



Mylocheilus, Agass. 



thanks to the numerous specimens collected by Lt. Trowbridge. The characters 

 of this genus are cs follows : Head elongated and sub-conical, rounded upon 

 the snout, which overlaps the lower jaw. The mouth is sub-terminal, horizontal, 

 of medium size and provided upon its angle with a maxillary barbel. The eye 

 is well developed. The isthmus rather narrow. The body is elongated, lance- 

 olated, compressed, sub-fusiform in profile. Pectoral fins slenderer than the 

 ventrals ; the latter being inserted in advance of the anterior margin of the dorsal. 

 Caudal fin furcated. Scales of medium size ; lateral line following the middle of 

 the flanks. The pharyngeal bones are stoutish, expanded upon their convexity, 

 with the inferior limbs very short. The teeth are inserted upon a very much 

 incliued plan, raised from the surface of the bone itself, from below upwards. 

 They are disposed upon two permanent rows of five and two, and a third decidu- 

 ous row of three in the thickness of the gum: 3 | 2 ] 5 5 | 2 | 3. They are of 

 the molar kind of the grinding type, but without grooves and ridges. 



1. Mylocheilus lateralis, Agass. & Pick. Amer. Journ. of Sc. 2d ser. xis. 

 1855, 231. 



Our specimens are from Fort Steilacoom, Puget Sound, W. T., and were col- 

 lected by Dr. Geo. Suckley, U.^S. A., under Gov. I. I. Stevens. 



2. Mylocheilus fratsrculus, is closely allied to the preceding by the shape 

 of its pharyngeal bones, differing from it by a more slender body, much smaller 

 head and smaller eye. The color is too far gone to have anything said about it. 



From Monterey, Cal., where specimens were collected by Lt. W. P. Trow- 

 bridge, U. S. A. 



3. Mylocheilus cauriicus. Cyprinus {Leuciscus) caurimis, Rich. Faun. Bor. 

 Amer. iii. 1836, 304. Has much of the general aspect of the two preceding 

 species, more, perhaps, of 31. fraterculus than 31. lateralis. The most prominent 

 difl'erence resides in the pharyngeal bones being less expanded upon the supe- 

 rior limb, which is much more developed also. The inferior limb is also more 

 slender. The head is more elongated, more conical than in 31. lateralis, and 

 larger than in if. fraterculus. The mouth is larger than in either of the two 

 species just referred to. 



From Astoria, 0. T.; numerous specimens collected by Lt. W. P. Trowbridge, 

 U. S. A. 



The genus we next introduce, and which has received the appellation of 



Mylopharodon, Ayres, 



is most closely related to 3Iylocheilus. The species which it includes are re- 

 markable for their elongated body, their sub-conical and tapering head, their 

 deeply cleft mouth, and, like the species of 3Ljlochcilus, they have the ventrals 

 inserted in advance of the anterior margin of the dorsal, the caudal furcated, 

 and a narrow isthmus. But 3Iylopharodon has no barbels upon either maxil- 

 laries or the angle of the mouth. The pharyngeal bones are likewise stoutish, 

 but tlie inferior limb is more elongated than in 3Tylocheilus, though a little 

 smaller than the upper limb. We observe the same system of dentition: an ex- 

 ternal deciduous row of two or three, and two permanent rows of two and four 

 or five : 2 I 2 I 5 5 | 2 | 2, or 3 | 2 | 4 4 | 2 | 3. But the crown is much more 

 compressed than in 3Iylocheilus. 



1. Mylopharodon conocephalus. Gila co7iocepliala, B. & G. Proc. Acad. Nat. 

 Sc. Philad. vii. 1854, 134. 



From San Joaquin River, Oal. Dr. Heermann. 



2. Mylopharodon robustus, Ayres, Pi-oc. Cal. Acad. Nat. Sc. i. 1855, 33. 

 San Francisco, Cah Dr. Newberry. 



