NATURAL SCIENCES OF PHILADELPHIA. 113 



compressis, obliquis ; lateralibus praelongis, lamellatis subcurvisque ; ruargarita 

 cajruleo-alba et valde iridescente. 

 Hab. Tombigbee River, Columbus, Mississippi. Wm. Spillman, M. D. 



Margaritaxa elliptica. Testa lasvi, elliptica, subinflata, subaequilaterali, 

 postice obtuse angulata ; valvulis ttmuibus ; natibus subprominentibus, ad 

 apices subconcentrice undulatis ; epidermide luteo-virente, glabra, nidda } 

 perradiata; dentibus cardinalibus parvis, compressis, in utroque valvulo singu- 

 lis; margarita. casruleo-alba et iridescente. 



Hab. Tombigbee River, Columbus, Mississippi. Wm. Spillman, M. D. 



Anodo.vta Texasensis. Testa, lajvi, elliptica, inflata, ad latere, rotunda, inae- 

 quilaterali, postice subangulata ; valvulis pertenuibus ; natibus subprominenti- 

 bus, ad apices biundulata ; epidermide dilute lutea, glabra, fulgida, obsolete 

 radiata; margarita caeruleo-alba, diaphana et valde iridescente. 



Hab. Texas. W. Newcomb, M. D. 



ICHTHYOLOGICAL NOTICES. 

 BY CHARLES GIRARD, M. D. 



XL1. Since we are again called upon to mention the genus Zygonecles, we will 

 venture to point out such structural peculiarities, as, in our opinion, may be 

 considered its generical characters. Body rather slender and elongated, com- 

 pressed, subfusiform in its profile, and covered with well developed scales. Head 

 rather small, depressed, subpyramidal. Mouth very protractile, its gape being 

 horizontal, whether in a protracted or a retracted condition. Teeth upon the 

 premaxillar bones and upon the lower jaw ; an external series slender and 

 acerated, behind which may be observed a band of velvet-like ones. The ori- 

 gin of the anal fin is opposite the anterior margin of the dorsal, or in advance 

 of it. The genus Zjigonect.es appears to be intermediate between Hydrargyra 

 and Gimbusia, resembling more the former by its general aspect, and the latter 

 by its structure. 



Specimens of a species of this genus, and which we call Z. pulchdlus, were 

 collected in Sugar Loaf Creek, Arkansas, by the party under Capt. A. W. 

 Whipple. The largest one measures two inches and a half in total length, of 

 which the head constitutes rather more than the fifth. The eye is large and 

 circular ; its diameter entering four times in the length of the side of the head. 

 The dorsal and anal fins are deeper than long ; the anal being larger than the 

 dorsal, and placed more anteriorly, so that its anterior margin is nearly equi- 

 distant between the apex of the snout and the posterior margin of the caudal 

 fin. The tip of the posterior rays of the dorsal extend as far as the insertion 

 of the caudal, that is, a little further backwards than the tip of the posterior 

 rays of the anal fin. The ventrals and the pectorals are but moderately de- 

 veloped ; the tip of the former extends to the vent, whilst the latter do not 

 quite reach the insertion of the ventrals. The ravs of the various fins are as 

 follows : D 9 ; A 12 ; C 3, 1, 7, 6, 1, 3 ; V 6 ; P 13. There are twelve longi- 

 tudinal rows of scales between the anterior margin of the dorsal and that of 

 the anal fin. The surface of the scales has a rather rugose appearance, owing 

 to the conspicuousness of the concentric lines of growth. The scales them- 

 selves are deeper than long, anteriorly subtruncated or subconvex ; undulating 

 and rounded off upon the remaining edges. 



The ground color is olivaceous brown, of a darker tint along the dorsal re- 

 gion than over the abdomen. A black band or streak extends from the nose, 

 across the eye, along the middle of the flank to the base of the caudal fin. 

 Small black dots, constituting four or five irregular longitudinal series, may bo 

 observed on either side of the dorsal region, above the lateral streak ; the 

 dorsal, anal, and caudal fins being likewise dotted with black, whilst the ven- 

 trals and pectorals are unicolor, like the abdomen. 



1859.] 



