36 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 21, 



would appear not to be sufficiently close, while the differences, on the 

 other hand, are too numerous to justify its arrangement in either of 

 these families. 



There is another Crustacean group, however, which presents a 

 much greater approximation to Himantopterus 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, dif- 

 fer 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 Eric- 

 thys 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 

 internal 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 Cuma, 

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

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

 toceros (and probably Cuma) exhibits very markedly that peculiar 

 sculpture which forms so prominent a feature of Himantopterus. 



The differences between these "Cumoid" crustaceans and the 

 latter genus consist principally in the shape of the antennae and the 

 development 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 Eric- 

 thys 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 Crus- 

 tacean of a similar character to these would produce a form wonder- 

 fully similar to Himantopteims. 



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. 



In their earliest condition these larvae possess sessile eyes, a short 

 carapace, a long jointed abdomen without appendages, and with the 

 terminal segment sometimes entire, sometimes bifid; the only append- 

 ages beside the minute trophi, consisting of a single pair of antennae 

 and a varying number of maxillipedes, so modified in form, as to serve, 



