PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. dl 
Tube of the anterior nostril half as long as the eye; the posterior 
nostril with a slight membranous expansion, not forming a tube; diam- 
eter of eye contained 24 times in the length of the snout, being placed 
nearly above the middle of the gape; gill opening slightly longer than 
the eye. 
Sides of the upper jaw with two series of teeth posteriorly ; the outer 
series small, close-set, somewhat triangular in form, slightly recurved, 
immovable; the inner series similar in form, but much larger, depressi- 
ble, the series not extending so far back as the outer and consisting of 
about five teeth; the two series separated by a well-defined groove; in 
front of these, and continuous with the outer series, are three nearly 
fixed knife-shaped teeth, the posterior the larger, next a movable tooth 
similar to the last fixed one but smaller, and three small fixed teeth in 
front. On the middle line of the vomer are three depressible, fang-like, 
arrow-shaped teeth, the first rather smaller than the largest lateral teeth, 
the, other two subequal and considerably larger, the posterior one very 
freely movable. These teeth are subject to some variation in different 
individuals, and are seldom quite alike on both sides of the same fish. 
In the lower jaw is a single series corresponding to the fixed series in 
the upper jaw. These are similarly enlarged in front, where the series 
is partly duplicated and some of the teeth are movable. The teeth in 
the lower jaw are broader and more directed backwards than those in 
the upper jaw. 
MYLIOBATID. 
48. Myliobatis californicus Gill. 
(Rhinoptera vespertilio Girard. ) 
The commonest of the numerous sting-rays in San Diego Bay. 
DASYBATID/:. 
49. Pteroplatea marmorata Cooper. 
Common in San Diego Bay. Probably distinct from P. hirundo, hav- 
ing a narrower disk and shorter tail, with distinct dermal fold above 
and below. 
50. Urolophus halleri Cooper. 
Common. This species is certainly not identical with U. torpedinus, 
in the synonymy of which species it is placed by Dr. Giinther. Its skin 
is entirely smooth. It is probably a valid species, more nearly allied to 
U. cruciatus than to U. torpedinus. 
51. Dasybatis dipterurus sp. nov. 
Allied to Dasybatis centrurus and D. pastinaca. 
Disk rhomboid, slightly broader than long; anterior margins nearly 
straight forwards, meeting in a very obtuse angle; posterior margins 
curved; lateral angles rounded. Tail nearly half longer than disk, with 
