182 U. S. p. R. R. KXP. AND SURVEYS — ZOOLOGY— GENERAL REPORT. 



horizontal one, particularly on the flanks. The dorsal groove^ as in Emhiotoca, extends to the 

 anterior articulated ray of the dorsal fin, but the sheath above it is much smaller, and formed 

 by one single row of rather small scales. There are no scales on the fins. 



DAMALICHTHYS VACCA, Grd. 

 Plate XXXIII. 



SrEC. Char. — Male provided with a sub-pyriform sac upon the anterior tliird of anal. BranchiostegaU five on cither side. 

 Ground color greyish olive. Scales with a golden and silvery metallic reflect Fins unicolor. 



SYN.—Damalkhthys vaca, Gru. in Proc. Acad. Nat. Sc. Philad. VII, 1855, 321. 



The head constitutes a little more than the fourth of the entire length. The snout is pro- 

 truding and sub-conical; the upper surface of the head is gently declivous, with a slight depression 

 above the orbital region. The eyes are sub-circular in shape, and their horizontal diameter is 

 comprised four times and a half in the length of the side of the head. The posterior extremity 

 of the maxillary does not reach the vertical of the anterior rim of the orbit. The teeth are 

 short and conical on the upper and lower jaw. The opercular apparatus is posteriorly rounded 

 and covered with rather large scales, disposed upon six obliquely vertical rows. The scales on 

 the sub-opercle are smaller, and disposed upon two longitudinal series. J There are four sub-con- 

 centrical rows of scales upon the cheeks, and somewhat smaller than on the opercle. The 

 supratympanic group is composed of about nine scales of the size of those occupying the ventral 

 region. The posterior limb of the pre-opercle is conspicuously developed. The branchiostegals 

 are five in niimber on either side. 



The upper outline of the body is gradually arched from the peduncle of the tail to the 

 occiput. The lower outline is less regular : from the chin to the origin of the anal the curve 

 is considerably depressed, raising rapidly along the base of the same fin. The peduncle of the 

 tail is elongated ; its depth equals the two sevenths of the greatest depth of the body, which is 

 the third of the total length. 



The origin of the dorsal fin is nearly opposite the anterior extremity of the base of the pec- 

 torals. It is gradually rising from the first to the last spine above which the anterior articu- 

 lated ray rises to twice again the height of that spine. The posterior articulated rays are about 

 the height of the third and fourth spines, that is, the fourth of the anterior ones. The upper 

 margin of that fin forms an open crescent. The rays themselves bifurcate but twice. The caudal 

 is deeply forked, and forming more than the si.xth of the entire length. Its rays subdivide five 

 times. The anal has the same general shape as the soft portion of the dorsal ; its external 

 margin forming an open crcBcent, but not so deep anteriorly, for its posterior rays have more 

 than the third of the depth of the anterior ones. Three small spines occupy its anterior margin, 

 which is situated under a vertical line drawn from the seventh articulated ray of the dorsal. 

 Next to the spines we meet with seven undivided rays, followed by twenty-six, which subdivide 

 three times. The base of that fin enters about five times in the whole leugtli, and, though 

 shorter than the soft portion of the dorsal, it extends a little more backwards. A pyriform 

 membranous sack exists upon the base of the undivided rays of the anal ; it is anteriorly perfo- 

 rated. The origin of the ventrals corresijonds to a vertical line drawn from the fourth dorsal 

 spine. Their extremity, when brought backwards, reaches the anterior articulated ray of the 

 anal. The rays exhibit traces of a division of the third degree. The pectorals are well devel- 



