56 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 84 



collected at Chame Point, Panama, by Robert Tweedlie. Cerdale 

 jioridana Longley was described in 1934 from several specimens col- 

 lected at Tortugas, Fla., in water not exceeding 10 fathoms in depth. 

 Five of these specimens are deposited in the National Museum col- 

 lections, and they represent the smallest species of the genus so far 

 reported. 



Unfortunately, the types of Cerdale ionthas Jordan and Gilbert and 

 of Microdesmus retropinnis Jordan and Gilbert were never received at 

 the National Aluseum, although they are recorded as having been 

 deposited there. M. retropinnis is represented in the National Mu- 

 seum collections by two examples, 85 and 99 mm in length, collected 

 in rocky tide pools at Chame Point, Panama. Of Cerdale ionthas we 

 liave two specimens from Panama, one collected by Gilbert and the 

 other by Tweedlie. 



The National Museum received a specimen of Microdesmus on 

 June 10, 1935, from Prof. Manuel Valerio, formerly director, Museo 

 Nacional, San Jose, Costa Rica. It was labeled "S. Lucas", and I 

 assume that it was collected on the Pacific coast of the Isthmus by 

 the donor. This specimen, 59 mm in standard length, proved to be 

 Microdesmus dipus Giinther, the second record of this rare fish. 

 Comparison of this specimen with the '^Microdesmus dipus" of Meek 

 and Hildebrand shows that the latter was erroneously identified, a 

 fact not wholly unsuspected by these authors. 



Careful study of the material before me shows conclusively that 

 Cerdale Jordan and Gilbert and Leptocerdale Weymouth are without 

 generic value, merely representing extreme specific variations mthin 

 the genus Microdesmus. Since Cerdale falls as a synonym of Micro- 

 desmus, the family name Cerdahdae must be changed to Micro- 

 desmidae. 



Our material shows conclusively that the characters of the branchial 

 openings, chiefly relied upon for differentiating between Cerdale Jor- 

 dan and Gilbert, Leptocerdale Weymouth, and Microdesmus Giinther, 

 are without generic value, being perfectly graduated between M. 

 jioridanus on the one hand and M. longipinnis on the other. The 

 point of origin of the dorsal fin is hkewise specific, M. aethiopicus 

 being intermediate between M. ionthas and M. retropinnis. The 

 genotype, M. dipus, is intermediate between M. ionthas and M. 

 longipinnis in all important external characters as well as the number 

 of vertebrae. 



It is evident from the wide distribution of the genus that only a 

 very small percentage of the species of Microdesmus are known at the 

 present time. The only species of which we have a fair series is the 

 one having the greatest number of rays in the vertical fins, and it is 



