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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Family VII. MYL10BATIDAE. The Eagle Rays. 
Disk broad; pectoral tins not continued to end of snout, but ceasing on sides of head and reap- 
pearing in front of snout as one or two fleshy protuberances (cephalic fins), which are supported by 
fin rays. Tail very long and slender, whip-like, with a single dorsal fin near its root, behind which 
is usually a strong retrorsely serrated spine. Nasal valves forming a rectangular flap, with posterior 
margin free, attached by a frenum to upper jaw. Skull less depressed than usual among rays, its 
surface raised so that the eyes and spiracles are lateral in position. Teeth hexangular, large, flat, 
tessellated, middle ones usually broader than the others. Skin smooth; no differentiated spines on 
pectorals in males, the sexes being similar. Ventrals not emarginate. Ovoviviparous. 
Only a single species of this family is yet known from Porto Rico. 
Aetobatina:: 
a. Teeth in a single series, very broad; muzzle entire Aetobatus, S 
RHINOPTERINiE: 
««. Teeth in several series, the middle series very broad. 
b. Muzzle entire Myliobatis 
bb. Muzzle emarginate; cephalic fins below level of disk Rhinoptera 
Fig. 4 . — Aetobatus narinari, dorsal view. 
Genus 8. AETOBATUS Blainville. 
General form of Myliobatis. Muzzle entire. Teeth flat, broad, forming a single series correspond- 
ing to the middle series in Myliobatis, there being no small lateral teeth. Upper dental lamina straight, 
lower curved and projecting beyond upper. Free border of nasal valve deeply emarginate. Skin 
smooth. Found in tropical seas. 
