200 A HISTORY OF RECENT CRUSTACEA 
carapace projecting ; the eye-stalks obscure, ‘immovably 
lodged in an orbit excavated in the dorso-frontal margin 
of the carapace, more or less covered by the antero-lateral 
margin of the carapace ;’ the second antenne terminating 
in a long and slender flagellum; the first four pairs of 
trunk-legs chelate ; the fifth pair simple in the male, some- 
times chelate in the female ; the pleon not longer than the 
carapace. The type-species, Polycheles typhlops, Heller, was 
first taken in the Mediterranean. Since then various species 
have been recorded from both the Atlantic and the Pacific, 
and from depths varying from 220 to 1,070 fathoms. Since 
in the female all the legs are usually chelate, the generic 
name, meaning ‘with many chele,’ is not inappropriate. 
Pentachéles, Spence Bate, 1878, meaning ‘ the creature 
with five chelze,’ seems to differ from Polycheles only in the 
particular alluded to in the generic name, the male in this 
instance, as well as the female, having the fifth pair of legs 
chelate. The genus has a wide range in both the great 
oceans, and the species descend to great depths. 
Spence Bate observes that Pentacheles euthrix (v. Wil- 
lemoes Suhm) has a close general resemblance to his own 
Polycheles baccata. 
Stereomastis, Spence Bate, 1888, is said to differ in 
nothing externally from Pentacheles, but to be established 
‘to receive those species in which the mastigobranchial 
lash does not exist.’ It was probably foreseen that some 
apology would be expected for such a definition, and the 
remark is accordingly appended, that ‘ difference of in- 
ternal structure as a specific character is of more value 
than any external distinction, which, though more con- 
venient for ciassification, is of little importance if it does 
not represent structural variation.’ Yet the example of 
the present genus gives but feeble support to this senten- 
tious aphorism, especially as in the two preceding genera 
the mastigobranchial lashes are for the most part of great 
tenuity, and in Stereomastis Suhmi, Spence Bate, the third 
maxillipeds have ‘a rudimentary mastigobranchial plate,’ 
though the trunk-limbs are without any. The meaning 
of the generic name would naturally imply the presence 
