106 
THE VOYAGE OF H.M.S. CHALLENGER. 
CYCLOMETOPA or CANCROIDE A. 
Cyclometopes, Milne Edwards (pt.), Hist. Nat. Crust., vol. i. pp. 264, 363, 1834. 
Cancroidea, Dana (pt.), U.S. Explor. Exped., vol. xiii., Crust. 1 , pp. 67, 142, 1852. 
Cyclometopa, Miers, Cat. New Zeal. Crust., p. 13, 1876. 
Carapace usually transverse, wide in front, with the antero-lateral margins regularly 
arcuated ; more rarely quadrate or suborbicular, but not rostrated. Epistoma short, 
transverse. Antennules usually transversely plicated. The exterior maxillipedes, the 
afferent channels to the branchiae, the branchiae, and the verges of the male are as in the 
Oxyrhyncha. 
Legion I. CANCRINEA or CANCROIDEA TYPICA. 
Gancrinea or Cancroidea typica, Dana, U.S. Explor. Exped., vol. xiii., Crust. 1, p. 145, 1852. 
This section, in Dana’s system, includes the whole of the typical Cyclometopa 
(Cancridae or Portunidae), which have almost invariably a littoral or marine habitat, and 
in which, therefore, the carapace is not antero -laterally convex and largely developed so 
as to constitute a vaulted respiratory chamber, as in certain Thelphusidae, which may 
remain for extended periods out of the water. The buccal cavity is usually well defined, 
and the flagella of the antennae are not greatly elongated as in those degraded forms 
(Corystoidea) which approach the Anomura. The dactyli of the ambulatory legs are 
styliform and unarmed, or in the fifth pair expanded into an ovate natatory organ ; 
they are rarely, if ever, armed with longitudinally seriate spinules as in those forms 
(Thelphusidae) which approach the Catometopa. 
Family 1 . Cancridm;. 
Canceriens, Milne Edwards (tribe), Hist. Nat. Crust., vol. i. p. 368, 1834. 
„ A. Milne Edwards (family), Ann. d. Sci. Nat., ser. 4, vol. xviii. p. 41, 1841 ; 
Nouv. Archiv. Mus. Hist. Nat., vol. i. p. 179, 1865. 
Cancridaz and Eriphidx, Dana, U.S. Explor. Exped., vol. xiii., Crust. 1, pp. 145, 147, 
228, 1852. 
Carapace, at least in the recent genera, transverse, usually convex, with the antero- 
lateral margins more or less arcuated, rarely subquadrate. Ambulatory legs all gressorial, 
with styliform dactyli ; species marine or littoral. 
The genus CEthra (the type of the section Canceriens cry ptop odes, Milne Edwards) is 
excluded, as being somewhat more nearly related to the Parthenopidse . 1 
1 Miers, Journ. Linn. Soc. Lond. (Zool.), vol. xiv. p. 669, 1879. 
