THE FISHES OF PORTO RICO. 
319 
Family LXXII. FIERASFERIDAt. The Pcarl-fishcs. 
Body elongate, compressed, tapering into a long and slender tail; no scales; teeth cardiform, on 
jaws, vomer, and palatines; canine teeth often present; no barbels; lower jaw included; vent at throat; 
gill-membranes somewhat united, free from isthmus; no pseudobranchiae ; no pyloric caeca; vertical 
fins very low, confluent, without spines; no ventral fins; pectoral fins present or absent. 
Small shore-fishes of tropical seas, often living in shells of mollusks, echinoderms, etc., being 
especially often commensal with the pearl oyster and with the larger Holothuria. Only one genus in 
American waters. 
Genus 154. FIERASFER Cuvier. 
Gill-membranes little connected, leaving isthmus hare. No distinct caudal fin; pectoral fins 
developed. 
The species of this genus are not well known, and their characters and nomenclatures are uncertain. 
It is not unlikely that the American species are all reducible to one, Fierasfer affinis or dubius, but our 
scanty material will not justify us in taking this view. (Jordan & Evermann.) Only one species 
known from Porto Rico. 
273. Fierasfer bermudensis (Jones). Pearl- fish. 
Head 8.5 in length; eye 4, longer than snout; mouth large, the maxillary reaching beyond orbit; ■ 
pectoral 2.5 in head. Teeth small, acute, uniserial, 3 in a line on vomer; palatine teeth small. Color 
pale-brownish, a bluish streak crossing nape between opercles, 4 pale points on back. Vertebrae 100. 
A small fish (length 3 to 6 inches) found in shallow water on coral shores in the West Indies. 
Two specimens, each about 4 inches long, obtained by us, one at Mayaguez, the other at Puerto Real. 
They certainly belong to the species described from Bermuda, which may not be different from 
Gunther’s F. affinis or Putnam’s F. dubius. 
f ? Fierasfer affinis Gunther, Cat., IV, 381, 1862, no locality given. 
? Fierasfer dubius Putnam, Proc. Bost. Soc. Nat. Hist. 1874, 344, Pearl Islands. 
Lefroyia bermudensis Jones, Zoologist, IX, 1874, 3838, Bermuda. 
Fierasfer bermudensis, Jordan & Evermann, 1. e., 2497, 1898. 
Family LXXIII. PLEURONECTID^. The Flounders. 
Body strongly compressed, oval or elliptical in outline; head unsymmetrical, cranium twisted, 
both eyes being on same side of body, which is horizontal in life, the eyed side being uppermost and 
colored, the blind side lowermost and usually plain. In the very young fish the bones of the head are 
symmetrical, 1 eye on each side, and the body is vertical in the water. In most species the eranium 
becomes twisted, bringing the upper eye over with it. Eyes large, well separated. Mouth small or 
large, the dentition various, teeth always present; premaxillaries protractile; no supplemental maxillary 
bone; pseudobranchise present. Gills 4, a slit behind the fourth; lower pharyngeals separate; no air- 
bladder; preopercle with its margin usually distinct, not wholly adnate or hidden by skin of head; 
vent not far behind head, viscera confined to anterior part of body. Scales various, rarely absent, 
usually small. Lateral line usually present, extending on caudal fin, sometimes duplicated or wanting. 
Dorsal fin long, continuous, of soft rays only, beginning on head; anal similar, shorter; caudal various, 
sometimes coalescent with dorsal and anal; pectorals inserted rather high, rarely wanting; ventrals 
under pectorals, usually of several soft rays, one of them sometimes wanting. 
Fishes mostly carnivorous, inhabiting sandy bottoms in all seas, some species ascending rivers. 
Many of them are important food-fishes. Genera about 55; species nearly 500. 
Subfamilies of Pleuronectidx. 
A. Ventral fins symmetrical, similar in position and in form of base, that of colored side not extended along ridge 
of abdomen. 
a. Mouth nearly symmetrical, dentition nearly equally developed on both sides, gape usually but not always wide. 
(Halibut tribe.) Hippoglossin^s 
aa. Mouth unsymmetrical, jaws on eyed side with nearly straight outline, bones on blind side strongly curved; teeth 
chiefly on blind side. 
b. Eyes and color on right side (with occasional exceptions) . (Flounder tribe.) Pi.euronectin.e 
AA. Ventral fins unsymmetrical, dissimilar in position and usually also in form, that of eyed side being extended along 
ridge of abdomen. Eyes and color on left side. (Turbot tribe.) Psettin.® 
