MYSIDACEAX CRUSTACEANS — TATTERSALL 533 



2403 (in the Gulf of Mexico) arc spinulose; on the other hand, I have 

 been unable to find any trace of spinules on the integument in speci- 

 mens from station 2314 (between Charleston and Savannab) and 

 station 2418 (between Cape Charles and Savannah). 



This character is not very satisfactory for specific purposes, for not 

 onl}?- is it very difficult to see, but it varies with the size and maturity 

 of the individual, the variance being more pronounced in the smaller 

 forms. At some stations where several animals were taken in a haul, 

 I found some spinulose and others apparently quite smooth. 



The variation in the armature of the telson throughout the collec- 

 tions was most noticeable. Faxon's type of longirostris has seven 

 lateral spines including the subapical ones on each side. In the 

 paratypes, I found usually four, but in two cases there was an addi- 

 tional notch that might indicate a fifth spine lost or in the process 

 of development. TattersalPs type of americanus had five, but in 

 material from other stations identified as americanus by Tattersall 

 and as typicus by Ortmann there are almost invariably four on each 

 side including the subapical one. 



After close examination of all the available material, I am of the 

 opinion that there are insufficient grounds for the separation of 

 americanus and that it should be regarded as a synonym of longirostris, 

 whose description should be amplified as follows: 



Carapace, integument smooth or more or less sparsely beset with 

 microscopic, forwardly directed spinules, especially in the dorsal 

 anterior region; rostral plate broadly tridentate with the central spine 

 produced into a long acute rostrum extending beyond the antennular 

 peduncle (rarely slightly shorter) but not extending to the tips of the 

 antcnnal scales; usually relatively longer in the female; posterolateral 

 angles produced into rather short acute spines. 



Antennular lamina well developed with inner margin usually 

 st raight, armed with a close row of long, very fine setae and terminating 

 in a strong tooth which extends very slightly beyond the apex; apex 

 rounded, armed with a regular row of small spinules (fig. \,aj). 



Antenna! scale of the rotundate type but less broad than in typicus; 

 outer margin armed throughout its length with from 6-8 strong 

 teeth; apex acutely pointed, straight or very slightly incurved (fig. lc). 



Tergal spines from the last abdominal somite long and acutely 

 pointed; from one-ninth to one-seventh as long as tho telson. 



Telson with lateral margins armed with 4-7 slender spines including 

 the subapical pair; apical spines very long (may be as much as one- 

 fourth of the telson in length) flanking a small apical plate bearing 

 5-8 small spinules (fig. l,b,e,h). 



