138 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.9 



A deep, double sheath of scales at base of anal fin. The proximal 

 sheath, which has a free straight edge exactly on the line of the ray- 

 bases, is composed of the lower row of modified supra-anal scales. The 

 second or distal sheath, entirely on the rays, is composed of two strong 

 rows of scales. Of these two rows, the visible sectors of the scales of the 

 proximal row are elongated obliquely in a dorso-posterior, antero-inferior 

 direction, while the visible sectors of the scales of the distal row are 

 elongated obliquely in a dorso-anterior, postero-inferior direction. After 

 approximately the seventeenth anal ray the distal one of the two rows 

 drops out, and the sheath is continued to the end of the fin-base by the 

 proximal row. This two-rowed distal sheath is very deep. Posterior to 

 the middle of the fin it extends halfway or slightly more to the tips of the 

 rays. The front part of the base of the dorsal fin shows an incipient sheath 

 of two to four small scales on the bases of the rays. 



In Jordan and Hubbs' key, Coleotropis starksi keys down to the 

 Thyrina group {Thyrina, Thyrinops, and Atherinella). It differs from 

 all of these in its much larger size, the more curved gape, the considerably 

 larger mouth (the maxillary reaching to below the front part of the eye), 

 and very sharply in the deep anal sheath. None of the Melaniris (=Thy- 

 rina, preoccupied^) group appears to possess any anal sheath at all. It 

 may be remarked that Melaniris brasiliensis possesses neither the pinched 

 belly nor the posteriorly produced air-bladder of the other species of 

 Melaniris, and it is a much larger fish. In these three characteristics bra- 

 siliensis resembles starksi, and it is possible that there is a close relation- 

 ship. M. brasiliensis, however, has no anal sheath and possesses the small 

 mouth of the other species of Melaniris. We therefore do not at this 

 time disturb its generic assignment. 



{Coleotropis, from KoAeos, 6, a sheath, and TpoTris, t), a keel, in refer- 

 ence to the scaly anal sheath.) 



Coleotropis starksi (Meek and Hildebrand) 



Menidia starksi Meek and Hildebrand, 1923, p. 267, pi. 20, fig. 2 (Ta- 

 boga Island, Panama Bay). 

 This species is known only from nine specimens from the Pacific coast 

 of Panama, preserved in the U. S. National Museum and Field Museum. 

 Through the kindness of Dr. L. P. Schultz, we have examined one of 

 the paratypes from Taboga Island in the National Museum (no. 79733). 



7 Thyrina Jordan and Culver 1895, is preoccupied by Thyrina Poujade 1886, 

 Ann. Societe Entomologique de France, sen 6, vol. 6, Bull., cxliii, a Lepidopteron. 

 The fish genus Thyrina must therefore be replaced by its synonym, Melaniris 

 Meek 1902. 



