A REVIEW OF THE MYSIDACEA 229 



Remarks. — This species differs from the generic description of 

 Diamysis in having only two sub joints in the sixth joint of the endo- 

 pods of the thoracic limbs instead of three and in having only one 

 joint in the exopod of the fourth pleopod of the male. It is, however, 

 so essentially a Diamysis in all its main characters that I have regarded 

 these differences as of only specific value. It differs from other species 

 of the genus, in addition to the two characters already mentioned, in 

 the many fewer spines on the margin of the telson, in the virtual ab- 

 sence of a rostral plate, and in the absence of spines on the inner uro- 

 pod. From the data accompanying the specimens this species, like its 

 congeners, lives in almost fresh water. 



Genus ANTROMYSIS Creaser 



Antromysis Creaseb, 1936, p. 121. 



The genus Antromysis was established in 1936 by Creaser for a small 

 but very interesting cave-dwelling mysid found in caves in Yucatan. 

 Unfortunately Creaser's account of the type species, A. cenotensis, 

 contains several serious errors of mysidacean morphology. He de- 

 scribes the mandibular palp as composed of two joints and figures it 

 as such (his fig. 22), yet in figure 15 he depicts correctly a 3-jointed 

 mandibular palp that he labels as the "first thoracic appendage (gnath- 

 opod)." The endopod of the true first thoracic appendage (fig. 13) 

 is labeled as the "second thoracic appendage (maxilliped)." The 

 true second thoracic appendage (gnathopod) is described as the "third 

 thoracic appendage (first true leg)," but in the text is referred to as 

 "following thoracic appendages," and moreover the exopodite is called 

 the endopodite and the endopodite the exopodite. Such grave mis- 

 takes make it difficult to decide how much reliance may be placed on 

 apparent differences between my specimens and Creaser's description, 

 whether such differences really exist or are the result of misinterpreta- 

 tions of the characters concerned. The most serious of these differ- 

 ences, and the most important because it is of generic significance, is 

 the form of the fourth pleopod of the male. In his generic definition 

 Creaser describes these appendages as biramous, the inner ramus com- 

 posed of two joints without lateral processes. In my specimens the 

 fourth pleopod of the male is biramous, but the inner ramus is com- 

 posed of a single flattened platelike joint with a well-marked setose 

 side lobe; it is in fact very similar to that described in so many 

 Mysidae. The outer ramus is, as far as I can make out, composed of 

 three joints terminated by a single strong barbed seta which is longer 

 than the combined length of the three joints of the ramus. If Crea- 

 ser's description of the fourth pleopod of the male is correct, the 

 differences I have pointed out would preclude the reference of my 



