208 [September, 



the presence of mitch smaller fin ; the anal Is a good deal smaller than the dorsal, 

 and the ventrals a little less anterior, with reference to the dorsal. 



D 10+2 ; A 8-f 2 ; 6, 1, 9, 8, 1,5; V 10+1 ; P 16. 



Upper regions of a greyish azur ; inferior regions dull silvery white ; black 

 dots scattered all over the back, sides and belly. 



Caught in Lost River, 0. T., by Dr. John S. Newberry, under Lt. R. S. 'William- 

 son, U. S. A. 



There is another generic type, for which we have provided the name of 



, SiBOMA, 



composed so far of but two species, one of which originally referred to the 

 genus Lavinia. It is to be recognized by a stout and somewhat compressed 

 body, covered with large scales. The caudal is crescent-shaped posteriorly; 

 the origin of the ventrals is situated a little posteriorly to the anterior margin 

 of the dorsal, or immediately under it. The head is rather small, sloping 

 towards a wedge-shaped snout, rounded superiorly. The mouth is of small 

 size, horizontal, terminal, with jaws even. No barbels. Eye below the me- 

 dium size. Isthmus rather narrow. Pharygngeal bones stout, expanded upon 

 their convexity, with the inferior branch short and bent inwardly so that its 

 extremity is directed outwardly, whilst the upper branch is slightly bent 

 inwards. The teeth are large and very compressed, and terminated by a 

 slender hook. They arc of the raptatorial kind, of the hooked type without 

 grinding surface properly so called, but instead of a sharp edge along the inner 

 margin of the teeth, a blunt and narrow ridge may be observed. They 

 are disposed upon a double row of one and two and four and five, as fol- 

 lows : 1 I 45 I 2. 



1. SiBOMA CRASSiCAUDA. Lavinia crassicauda, B. & G. Proc. Acad. Nat. Sc. 

 Philad. viii. 1854, 137. 



Specimens of this species were procured by Dr. A. L. Heermann, under Lt. 

 R. Williamson, in the San Joaquin, Mercede and Mohave Rivers, Cal. 



2. SiBoifA ATRARiA. The largest specimen of this species which we have ex- 

 amined is about seven inches in length, and although small, compared to the 

 specimens of S. crassicauda, to which we had to compare it, yet the distinctive 

 features between the two species appear very striking. And first of all, the 

 imbrication of the scales in S. atraria, is such as to expose more of their surface 

 than in S. crassicauda, and moreover the lateral line in S. atraria runs along 

 the seventh row of scales from the insertion of the ventrals upwards, leaving 

 eleven rows above it, to the base of the dorsal fin, Avhilst in ^S'. crassicauda, there 

 are as many rows of scales below as above the lateral line. The absolute 

 number of longitudinal rows of scales is the same in both species. The head 

 is proportionally larger than in S. crassicaudu, but the fins are much less de- 

 veloped. The ground color is olivaceous, the sides and the back being nearly 

 black or brownish black, from the number of confluent maculae and dots. 

 The fins itself are blackish upon an olivaceous ground. The sides and upper part 

 of the head, arc likewise brownish black. 



Found in a spring, in Utah District, near the Desert, by Lt. E. G. Beckwith. 



The species which are arranged under the genus 



Ptyciiochkilus, Agass. 



remind us by their general appearance of both 3Iylocheilus and Mylopharodon. 

 They have an elongated, subcylindrical and compressed body, an elongateel 

 head, a mouth deejily cleft, but no barbels upon its angle. The upper jaw 

 overlaps the lower, though the mouth remains horizontal and subterminal. 

 The eye is of moderate size; and so with the isthmus. The ventral fins are 

 inserted a little in advance of the anterior margin of the dorsal. The caudal 

 is furcated. The scales,. of medium size ; the lateral line nearly medial. The 



