new Species of Platjsomus. 253 



are placed opposite to each other, terminating in front of the 

 caudal peduncle, and anteriorly near the centre of the body ; 

 the anterior portion of each is considerably prolonged, and the 

 articulations of the rays are much longer than wide. The 

 caudal fin is well developed, with the lobes, which are nearly 

 of equal length, only slightly recurved at the extremities. 



The scales (PI. XVII. fig. 2) are rhomboidal, long, narrow, 

 and exceedingly delicate, the thickening of the anterior margin 

 being very inconspicuous at the surface, so that the usual 

 ribbed appearance is scarcely observed : the upper surface is 

 finely and regularly striated longitudinally, the striaj being 

 raised a little, undulated, and almost parallel to the margins of 

 the scale ; they occasionally bifurcate, and, though minute, 

 are relatively strong and few in number, there being not more 

 than eight or ten on each scale. The length of the scale, in- 

 cluding the peg, is five sixteenths of an inch ; the peg is long 

 and pointed. The occipital crest, all the bones of the head, 

 gill-covers, clavicle, and mandibles are striated in the same 

 manner as the scales. The mandibular teeth are minute, 

 conical, and pointed ; those of the maxillaries are of the same 

 character, but more minute ; on the premaxillaries they seem 

 a little larger. 



This is a very distinct species, and is at once distinguished 

 from P. striatus by its small size and the much greater deli- 

 cacy of its parts : the scales of striatus are wide, thick, and 

 coarse in comparison with those of P. rotundus^ in which they 

 are thinner and much narrower than in any other species with 

 which we are acquainted ; and, moreover, the striae in P. stri- 

 atus are much more numerous and more oblique. The same 

 features equally distinguish our new species from P. gihbosus, 

 which is apparently a close ally of P. striatus. On account 

 of its small size, it might possibly be confounded with P. par- 

 vulus : but the scales of the latter are twice the width of those 

 of the former, and the striaj are much more numerous ; the 

 head-bones, too, are tuberculated, while in P. rotundus they 

 are, as we have already pointed out, striated ; the teeth of P. 

 jjarvulus are likewise considerably larger. 



Of the inedited species P. declivis^ Agassiz, we know very 

 little, but understand that the scale is similar to that of P. 

 striatus ; the name, too, so far as it is descriptive, is certainly 

 not specially applicable to P. rotundus. 



this opportunity of stating that a specimen of P. parvidus in our possession 

 displays distinctly the pectoral, ventral, and anal fins, the form of one 

 of the veutrals being well defined : it is smaU and narrow. 



