GILBERT AND STAEKS — FISHES OF PANAMA BAY 



195 



Family CERDALID^. 

 344. Microdesmus dipus Gii-nther. 



Not seen by us. In addition to the type, this species is known only from a 

 specimen recorded by Lockington (1881, p. 114), from La Paz, L. C. 



Dr. G. A. Boulenger has kindly re-examined for us the type of the species, 

 and writes: " There are four ventral rays. The fifteen anterior dorsal rays are 

 simple and inarticulate; further back they gradually become branched and articulate, 

 and are distinctly so from the eighteenth. The anal rays are all articulate and 

 branched." 



345. Microdesmus retropinnis Jordan S Gilberl. 



Platk XXXI, Fig. 59. 



Seven specimens were obtained in rock-pools on the Panama reef. 



The genus Microdesmus — with the two species M. dipus and M. retropinnis — 

 has been described as having the ventrals reduced each to a single ray. Our 

 material has shown, however, that in M. retropinnis a serious error was committed, for 

 each ventral fin consists of a short slender spine and three slender unbranched rays, 

 the inner of which is the longest. Through the great kindness of Dr. G. A. 

 Boulenger, who has examined for us the type of M. dipus, we learn that that species 

 also has "four ventral rays" (undoubtedly one spine and three rays). 



In M. retropinnis, the dorsal fin contains 15 slender spines and 32 to 34 rays. 

 Each of the rays is definitely articulated, and the majority of them are many times 

 forked. The anal rays are all articulate and all but the first one forked. 



We are informed by Dr. Boulenger that in M. dipus also the fifteen anterior 

 dorsal rays are simple and inarticulate, while further back they gradually become 

 branched and articulate, being distinctly so. from the eighteenth back. In this species 

 the anal rays are all articulate and branched. 



In one specimen of M. retropinnis, we enumerate 58 vertebrsE in addition to 

 the hypural element. The latter is assisted by one spine in forming the basis for 

 attachment of the caudal fin. 



In six specimens the fins count as follows: 



Dorsal.. 

 Anal ... 



47 

 29 



The scales are circular in outline, attached by their entire margin, and are 

 non-imbricate. On the head and the anterior part of the body, they are closely 

 crowded and are arranged in definite rows. Toward the tail, they are moi'e widely 

 spaced, and on the abdomen they are partially or wholly embedded and difficult to 

 detect. They cover the entire head, including snout and branchiostegal membranes. 



The margin of the upper jaw is formed by the premaxillaries, the broad max- 



