88 L. Agassiz on the Ichthyological Fauna of Western America. 
which I shall call Morostoma tenue, as it differs from the others, 
by its more yey sapier form, and less prominent differences be- 
tween males and females. I would unhesitatingly refer also Ca- 
tostomus congestus, B. ee G., to this geuus, from the characters 
assigned to this species, were the oo line et described as run- 
ning straight along the middle of the side, when the absence of 
a lateral line is the most prominent character ‘of the genus Moxos- 
toma. Not having however seen a specimen, I must leave it for 
Messrs. Baird and Girard to determine whether it is a genuine Ca- 
tostomus, as the genus is now circumscribed. 
Ptychostomus, Agass. 
In respect to form of body and the structure and position of 
fins, this genus does not differ from Catostomus proper, but may 
be distinguished by the following structural peculiarities. The 
lips are marked by transverse ridges or folds, and hardly bileiess 
below; they are not papillated as in Catostomus proper. 
generic name of this type is derived from this character - _ 
lips. ‘The head is shorter and stouter. The dorsal is longer than 
it is high, but in the males it is longer in proportion than in the 
females. The anal of the male is also broader than that of the 
female, and its lower margin lobed, while in the female it is tra- 
pezoidal and narrow. Such differences between the sexes do not 
exist in the species of Catostomus pro 
The scales are as large on the anterior as on the posterior parts 
of the body; their vertical diameter about as great as the longi- 
tudinal, so that the scales are nearly quadrangnlar with rounded 
edges ; the ornamental concentric ridges not longer nor broader 
n the posterior than upon the lateral and anterior fields; the 
radiating furrows few, only one or two in the posterior field, and 
one on each side, limiting that field from the lateral fields; those 
of the anterior field are more numerous, and yet not crowded. 
Tube of -the lateral line arising in the centre of radiation or far- 
ther back upon the posterior field 
The pharyngeals are strong, their entire edge spreading like a 
wing, and that spreading margin is sep- 
arated from the symphysis by a deep 
emargination. The teeth, increas- 
ing rather rapidly in size from above 
ownwards, are more apart from one 
another than in the preceding genera, 
and arched inwards as in Moxostoma ; 
the inner edge of the lower ones 
square, its inner margin rising into a 
broad cusp in the middle and upper 
teeth. Fig, 6, 4 Ce the nght 
a of Ptychostomus macro- 
ous from its inner surface, Hone of the lower teeth, e aad d 
tooth {rele the middie and “Upper part of the arc’ 
>. 
