184 [September, 



The lengthy description appended to it, reminded me very forcibly of those " spe- 

 cific descriptions referring chiefly to individual peculiarities of specimens, a kind 

 of portrait of peculiar individuals without much likeness."* After a careful 

 study of whatever specific there was in the description of Acrocheilus alutaceus, I 

 came to the conclusion that Acrocheilus was identical with 



Lavinia, 



published for the first time in 1854, nearly one year before Acrocheilus was pro- 

 posed. Circumstances of that kind are always to be regretted on eitber side. 

 The characters of the genus are as follows : The body is very much compressed, 

 deep, subfusiform in outline, covered with well developed scales ; the lateral line 

 forming an open curve, convex downwards, nearer the abdominal outline than the 

 back. The fins are well developed ; the insertion of the ventrals are situated 

 either in advance of the anterior margin of the dorsal, or immediately under it. 

 The posterior margin of the dorsal approximates more or less the anterior mar- 

 gin of the anal. The caudal is deeply furcated, rounded upon its insertion, and 

 provided with numerous well-marked rudimentary rays above and below. The 

 head is rather small. The cleft of the mouth is situated altogether anteriorly to 

 the crbit ; it is of medium size, the upper jaw overlapping the lower one, which 

 is either rounded or truncated upon its symphysis. There are no buccal barbels. 

 The eye is of moderate size ; a narrow isthmus separates the gill openings. The 

 pharyngeal bones are strongly curved, the upper branch directed inwards and 

 downwards, the inferior one slightly arched backwards, with the convexity di- 

 lated. The teeth, being of the cultriform kind of the grinding type, and dis- 

 posed upon one single series of five, thus : 5 5, with a sharp terminal 

 point. 



1. Lavinia exilicauda, B. & G. Proc Acad. Nat. Sc. Phila. vii. 1854, 137- 

 Lavinia compressa, Ayres, Proc. Cal. Acad. Nat. Sc. i. 1855, 21. 



From Sacramento River, Cal. ; collected by Dr. A. L. Heermann. 



2. Lavinia alutacea. Acrocheilus alutaceus, Agass. & Pick. Amer. Journ. of 

 Sc. 2dser. xix. 1855, 99. 



From Willamet Falls and Wallawalla river, collected by Dr. Charles Pickering, 

 under Capt. C. Wilkes, U. S. N. 



3. Lavinia haeengtjs. This species is intermediate between L. exilicauda and 

 L. alutacea. The most characteristic feature consists in the relative position 

 of the dorsal and anal fins, which are wider apart. Their size is nearly the same, 

 and if any difference should be observable, the anal would be found a little lar- 

 ger than the dorsal. The specimens before us are in a mutilated condition, inas- 

 much as the scales are all fallen. The dorsal region seems to have been of a 

 much deeper hue than the lower half of the sides, which are whitish, as well as 

 the belly, contrasting with the rather dark hue of the dorsal region. 



Caught at Monterey, Cal., by A. S. Taylor, Esq. 



IV. 



This fourth group is less uniform, if the teeth are taken into account. The lat- 

 ter belong to the hooked types, with or without grinding surface {Denies unci- 

 nato-submolares a,ndu7icinato-subconici), of the raptatorial [Denies raptaiori) and pre- 

 hensile {D.prehensiles), kinds chiefly; in most cases disposed upon a double series. 

 But all its representatives are provided with buccal or maxillary barbels. In 

 the species from the Pacific range a thin cartilaginous pellicle is observed upon 

 the jaws : illustrating what we had already remarked, that the cartilaginous lips 

 are not sufficient to characterise the group of Chondrostomi. Of course, it is in 

 the latter where that character assumes its greatest developement. 



*Amer. Journ. of Sc. 2d. ser. xix. 1855, 220 



