ON THE STRUCTURE AND AFFINITIES OF ' HIMANTOPTERUS 447 



There is another Crustacean group, however, which presents a 

 much greater approximation to Hiniantopterus in some of its forms, — 

 the family of the Stomapods. 



This small and not very well-defined group occupies nearly a cen- 

 tral position among the Crustacea ; and its members, like those of 

 most central groups, while presenting a strong general similarity, 

 differ very widely in details. The genus usually regarded as the 

 type of the family — Squilla — is not more like Himantopterus than an 

 ordinary Macruran would be ; but if we turn from Squilla to Ericthys 

 and Mysis, and thence to Cuma and its allies, we shall find we have 

 passed by a series of insensible gradations from the close ally of the 

 Podophthalmous Macrura to a sessile-eyed Crustacean, with the in- 

 ternal antennae almost rudimentary, with a very small carapace, like 

 that of a Copepod in its proportions, and with twelve free segments, 

 the anterior of which only carry appendages, all the abdominal ones, 

 except the penultimate, being in some cases deprived of them. 



The characters just mentioned are common to the genera Cuvia,^ 

 Bodotria, Alauna, and Calyptoceros (the last a new genus lately 

 discovered by myself in the Bristol Channel) : and, in addition, Calyp- 

 toceros (and probably Cuina^ exhibits very markedly that peculiar 

 sculpture which forms so prominent a feature of Hiviantopterus. 



The differences between these " Cumoid " crustaceans and the latter 

 genus consist principally in the shape of the antenns and the develop- 

 ment of the thoracic appendages in the former, each thoracic segment 

 being provided with a pair of simply constructed members. In addition 

 there is a pair of appendages to the penultimate abdominal segment, 

 of which no trace has been found in Himantopterus. 



As regards the two former discrepancies, however, we find in Erictliys 

 that the three posterior pairs of thoracic appendages are reduced to 

 mere rudiments, even the two pairs which precede them being very 

 small. The largest of all the thoracic appendages are the first and 

 second maxillipedes, the former being terminated by an oval plate- 

 like joint. The external antennae carry a similar oval plate on a 

 long stem. 



Reductions and modifications of the appendages of a Cumoid 

 Crustacean of a similar character to these would produce a form 

 wonderfully similar to Himantopterus. 



But such reductions and modifications carried still further, and 

 bringing us still nearer the ancient form, are to be met with, not, 

 indeed, in any adult Crustacean at present known, but in those 

 remarkable larvae of the Podophthalmous Malacostraca which were 

 once known under the name of Zocea. 



