374 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



ring at the base of pectorals inclosing a large sub-circular black spot. Beneath dull yellowish 

 white ; the external margin of the ventrals being blackish. The dorsal fins are olivaceous ; 

 the extremity of the tail blackish with a lighter margin. 



List of specimens. 



Family MYLIOB ATIDAE , Owen. 



The rays of the pectoral fins disappear altogether on the sides of the head, but develop again 

 in front of it, constituting a kind of cephalic fin, which forms the anterior extremity of the 

 disc. The head, therefore, from the region occupied by the spiracles forwards, is separated 

 from the discoid body ; it is likewise more developed than in the other families of this sub-order. 

 The nasal flaps of either side coalesce into a quadrilateral, posteriorly fringed membrane, or 

 lip, which extends to the mouth. The nasal apertures approximate interiorly, being separated 

 by a narrow frenum, which tapers away towards the angles of the mouth. The latter is 

 straight. The dentated portion of the jaws extends deep inwardly. The teeth are large, 

 depressed, mosaic pavement-like. The upper maxillar membrane extends from the palate and 

 the cheeks outwardly, it being very long, with a convex margin, which is fringed upon its 

 middle. The lower maxillar membrane is close to the dental margin. Behind these membranes 

 may be observed some papillae still. The eyes and the spiracles are situated on the side of 

 the skull ; the spiracles being separated from the eyes by a wide bridge. The eyelids are 

 wanting. The tail is^elongated, flagelliform, with a dorsal fin at its base, and a depressed 

 spine behind the latter, directed horizontally backwards. 



SYN. jMyliobatini, BONAP. Syst. Vertebr. 1837, 44; &, Selach. Tabul. analyt. 1838, 3. Bd. Iconogr. Encycl. II, 1850, 243. 

 Myliobatides, MULL. & HENLE, Syst. Beschr. Plagiost. 1841, 176. MULL, in Wiegm. Archiv fiir Naturg. 1845, I, 137. 



BUM. Ichthyol. analyt. 1856, 145. 

 JUyliobatidae, OWEN, Lect. Comp. Anat. Vertebr. Anim. 1846, 51. 



The Myliobatides are quite numerous along the Atlantic coast of the United States, where we 

 find species of Myliobatis, of Aetobatis, and Shinoptera, the chief representatives of this family. 



RHINOPTERA, Kuhl. 



GEN. CIIAU. Snout more or less emarginated anteriorly. The cranial fin not in a same level with the pectorals, being 

 directed more downwards, and fixed to the inferior edge of the base of the pectorals. The rays of the cranial fin begin, 

 likewise, more backwards than the termination of the rays of the pectorals. The lower edge of the nasal flap is straight, 

 whilst its exterior angle is pointed. On the dorsal surface a longitudinal fissure on either side. Either margin of the jaws 

 straight. The teeth are broader than long, hexagonal, depressed, placed side by side, constituting from three to five series, 

 diminishing in size laterally. Alongside and exteriorly to the former there are a few series of smaller teeth, not broader 

 than long ; they occupy the entire width of the jaws. 



SYN. JRhinoptera, KUIIL, MULL. Yergl. Anat. Myxin. I, ,.1836, 76. MULL & HEXLE, Syst. Beschr. Plagiost. 1841, 

 181. DEKAY, New Y. Faun. IV, 1842, 375, STOKER, Synops. 1846, 263. BUM. Ichthyol. analyt. 1856, 

 145. 



Whenever an opportunity shall be afforded us for comparing the species from our Atlantic 

 cuast to the one recorded hcreon, we may be better prepared in pointing out the characters which 



