32 
W. M. TATTERSALL. 
Sub-Family Mysidetina;, Holt and Tattersall. 
Genus Mysidetes, Holt and Tattersall. 
? Mysidopsis, G. 0. Sars, 1883 and 1885, non G. 0. Sars, 18G4. 
Mysideis (pars'). Holt and Tattersall, 1905, non G. 0. Sars, 1869. 
Mysidetes, Holt and Tattersall, 1906 (1) and (2). 
Metamysidella, Illig, 1906. 
A full diagnosis of this genus and a statement of its possible affinities have 
already appeared, Holt and Tattersall (1906 (2)). While agreeing in most characters 
with the normal genera of the Leptomysince, the rudimentary nature of the pleopods 
of the male offers a feature of sharp distinction from members 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 Heteromy.sis and Mysidella, but whereas in the former the third, and 
in the latter the first, thoracic limbs are peculiarly 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 respective characters was given (Holt and 
Tattersall 1906 (2)). It will suffice here to mention that Mysidetes differs from 
Mysidopsis, (1) 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 the first thoracic limbs seven- 
jointed instead of six. 
From Mysideis it is distinguished by 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, (l) 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 belongs to this genus. It was 
described in the ‘ Challenger ’ Report from a specimen taken off Australia. 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, 1906) is undoubtedly synonymous with this 
genus, though no mention is made in the diagnosis of the character of the pleopods of 
the male. In all other features the two genera agree absolutely. 
O O n 
