THOMPSON: A RARE THALASSINID. 
19 
Thaumastocheles is rather Nepkropsidean in its characters. Both 
Calocaris and Calliaxis, on the other hand, are more Thalassinoid, 
and Ortmann (’ 98 ) recently has separated the genera, placing 
Thaumastocheles in the Nephropsidea, Calliaxis and Calocaris to¬ 
gether with Laomedia in the family Axiidae of the Thalassinidea. 
This classification is in perfect accord with the Axiid affinities of 
Calliaxis’ ally, Naushonia. And although it must not be regarded 
as at all final, it may well be accepted as more natural than any 
other arrangement which is possible at present. 
There is great need, however, for a thorough revision of the 
Thalassinoid Crustacea, and until that is made, the relations of 
the genera to one another must remain obscure and any separation 
into families be more or less tentative. Ortmann distinctly states 
this in connection with the systematic arrangement just cited (’ 98 , 
p. 1141). Such a welcome aid to research, however, cannot be 
attempted as yet. It must await a more ample knowledge of the 
anatomy of the individual forms, and all study should hold that 
end in view. The present article, then, only attempts to give an 
account of two of the more imperfectly known genera of the 
Thalassinidea and of the remarkable character of their larvae. Of 
these, Calliaxis is probably to be regarded as the more specialized 
since it has a reduced antennal scale, small mastigobranchs, weaker 
epimera, and more perfectly formed chelicipeds. In its develop¬ 
ment, also, its larvae present the strange form to a greater degree 
than do those of Naushonia; the metamorphosis is slightly more 
concentrated, the fourth pereiopods never having functional exo- 
j)ods; and the peculiar ventral gland is larger. 
The establishment of the true position of these genera within the 
Thalassinidea must be left to future students. But it seems proba¬ 
ble that research will tend to intensify rather than to diminish the 
differences that separate them from other members of the group. 
Calliaxis and Naushonia may be regarded as aberrant forms, proba¬ 
bly from pre-Axiid stock, which have retained characters that ally 
them on the one hand to the more primitive Axiidae and on the 
other suggest relationship with genera of the Nephropsidea. And 
their evolution has been along lines apart from that of most 
Thalassinids, especially in the development of the very unusual 
larval form. 
