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. 
Catal 
No. 
No. of 
spec. 
Age. 
Locality. 
When col¬ 
lected. 
Whence obtained. 
Nature of 
specimen. 
Collected by— 
9S9 
i 
San Francisco, Cal... 
1853 
Lieut. J. G. Parke _ _ 
Alcoholic_ 
Dr. A. L. Heermann. 
990 
i 
Young. 
! Presidio, Cal- 
1853 
Lieut W. P. Trowbridge 
_do. 
Lieut. Trowbridge . 
Family MYLXOB 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. — Myliobatini, Bonap. Syst. Vertebr. 1837, 44; &, Selach. Tabul. analyt. 1838, 3.—Bd. Iconogr. Encycl. II, 1850, 243. 
Myliobatides, Mull, & Henle, Syst. Bescbr. Plagiost. 1841, 176.— Mull, in Wiegrn. Archiv fur Naturg. 1845, I, 137. 
Dust. Ichthyol. analyt. 1856, 145. 
Myliobatidae, 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 Aiitobatis, and Bhinoptera, the chief representatives of this family. 
RHINOPTERA, Kuhl. 
Gen. Ciiar.—S nout 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.g- 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. — Rhiroptera, Kuhl,—Mull. Vergl. Anat. Myxin. I, t 1836, 76.— Mull & Henle, Syst. Beschr. Plagiost. 1841, 
181.— DeK ay, New Y. Faun. IV, 1842, 375,— Storer, Synops. 1846, 263.— Dum. Ichthyol. analyt. 1856, 
145. 
Whenever an opportunity shall be afforded us for comparing the species from our Atlantic 
coast to the one recorded hereon, we may be better prepared in pointing out the characters which 
