32 AV. .M. TATTEKSAI,L. 



Sub-Family ^Iysidetin.k, Holt and Tattersall. 

 Genus Mysidetes, Holt and Tattersall. 



? Mi/sidopsis, G. 0. Sars, 1888 and 1885, noii G. 0. Sars, 18G4. 

 M//sideis (pars), Holt and Tattovsall, IDd.j, iinn 0. 0. Sars. IkC,;). 

 Mysidetes, Holland Tattersall. llloC (1) and (2). 

 Metfimi/sidclhi, Hlig, \'Mh\. 



A full diagnosis of this genus and a statement of its possible affinities have 

 already appeared, Holt and Tattersall (1906 (2)). Wiiile agreeing in most characters 

 with tlio normal genera of the LcptoinyMlnai, the rudimentary nature of the pleopods 

 of the male otters a feature of sharp distinction from meml)ers of that sub-family 

 and has necessitated the establishment of a new sub-family for its reception. In 

 the form of the telson and armature of the inner uropods it approaches rather closely 

 to the genera Heteromysis and MysidcUa, but wliereas in the former the third, and 

 in the latter the first, thoracic limbs are jieculiarly modified and strongly armed, in 

 Mysidetes both these limbs are of normal structure. The external resemblance of 

 females of the present genus to those of Mysidopsis and Mysideis has already been 

 noted, and a comparative table of their resjjective characters was given (Holt and 

 Tattersall 190G (2)). It will sufiice here to mention that Mysidetes differs from 

 Mysidopsis, (l) in having a well-developed molar tubercle to the mandible; (2) in 

 the presence of a setiferous expansion of the inner margin of the basal part of the 

 second maxilla, and (3) in having the endopods of tlie first thoracic limbs seven- 

 jointed instead of six. 



From Mysideis it is distinguished l)y having the endopods of the first and 

 second thoracic limbs of normal stoutness and usual armature, instead of being 

 unusually massive and strongly armed; while from both genera it differs, (1) in 

 having the cleft of the telson armed with spines ; (2) in the uropods having a row 

 of spines in their inner edges extending well over half-way down their length, and 

 finally, (3) in having the pleopods of the male rudimentary. 



Mysidopsis incisa, G. 0. Sars (1885), probably Ijelongs to this genus. It was 

 described in the ' Challenger ' Report from a specimen taken off' Austraba. This 

 specimen is a female much mutilated, and dissection was neither practicable nor 

 desirable. The telson and inner uropods, however, conform to the type found in 

 Mysidetes. 



The genus Metamysidella (Illig, 190G) is undoubtedly synonymous with this 

 genus, tliougli no menticm is made in the diagnosis of the charac'ter of tlic pleopods of 

 the male. In all otlier features the two genera agree absolutely. 



