REPOET ON ICHTHYOLOGY. 407 



The head is small, forming- about a fifth of the entire length; it is oblong-conieal 

 in profile, and the cranium is wide, the width of the occipital region being only about 

 a third less than the length of the naked dorsal surface. 



The snout is moderately depressed and prominent. 



The eyes are of moderate size, lateral hut superior, and entirely in the anterior 

 half of the head. 



The mouth is rather broad, but of moderate size, the maxillary bones ceasing 

 under the anterior borders of the orbits; the lower closes within the upper. The 

 lower lips are separated at the symphysis by a wide isthmus. 



Barbels of moderate size are present at the angles of the mouth. 



The branchial apertures extend forward to the vertical of the preoperculunu and 

 are separated by a narrow isthmus. 



The dorsal fin commences nearly midway between the snout and base of caudal. 

 It is subquadrate, and has about ten rays; the first three are slender and spinous; the 

 anterior spine rudimentary. 



The anal fin is similar in size to the dorsal, and is intermediate between the bases 

 of the ventral and caudal fins. 



The pectoral fins are subfalciform, the first rays being longest. 



The ventral fins are triangular, and situated under the dorsal fin. The axillary 

 scales are elongated, but not pointed. 



The caudal fin is forked and its lobes are equal. 



The pharyngeal bones are rather stout and expanded at their angles; the peduncle 

 quite short. The teeth are well developed, much compressed, and furnished with 

 narrow grinding-surfaces; they are in a double row, four in the primary and one in 

 the secondary. 



The form which we have above characterized is at least as well entitled to a 

 generic separation from the Pogonkhthys as typified by the Pogonkhthys inaequilobus of 

 Girard as many of the genera of Cyprinoids distinguished by naturalists. The only 

 species at present known to belong to the genus is that which has been described by 

 Dr. Girard as Pogonkhthys communis. From the other species of the genus Pogonkhthys, 

 it is distinguished by its broad and flattened head and muzzle, the very gradual decrease 

 in width of the cranium, and the large scales. It is also worthy of note that all the 

 typical Pogonkhthyes are inhabitants of California, while the Pogonkhthys communis is 

 found in the country east of the Rocky Mountains. 



The genus Platygobio belongs to a group of nearly allied genera, comprising 

 especially Gobiooi Cuvier, Semotilus of Rafinesque, Pogonkhthys of Girard, and Ahjoma 

 of Girard. Some of these genera have been widely removed from each other, but all 

 of them appear to be very closely allied. It certainly cannot be in conformity with 

 nature to place genera at almost extremes of the family simply on account of the pres- 

 ence or absence of barbels and the presence of one or two rows of pharyngeal teeth. 

 Such are scarcely generic characters alone, and the latter character especially appears 

 to be inconstant, the second row being perhaps deciduous. At least, there are fishes 

 that have been placed in different genera on account of the presence or absence of the 

 inner row of two or three small teeth, which can scarcely be even specifically, much 



