REPORT ON THE BR ACHY UR A. 
•209 
the flagellum is obsolete. The ischium-joint of the endognath of the exterior maxilli- 
pedes is much longer than the merus, and very slightly produced at its antero-internal 
angle, the merus is small, distally truncated, very slightly emarginated or obliquely 
truncated at the antero-internal angle, and the antero- external angle is not produced. 
The chelipedes (in the adult males at least) are unequal and well developed, or rather 
large, the joints are smooth, without spines ; palm of moderate length, rounded above ; 
fingers rather shorter than the palm, with the teeth of the inner margins small or 
sometimes indistinctly developed ; in the larger chelipede the dactyl is arcuated, and the 
fingers have between them a wide intermarginal hiatus. Ambulatory legs of moderate 
length, with the joints smooth without spines ; dactyli terminating in a strong arcuate 
claw. 
The type species of this genus, Acanthocyclus gayi ( = Acanthocyclus villosus, Strahl; 
Plagusetes ela tus, Heller) occurs commonly on the shores of Chili and Patagonia, and in 
the Magellan Straits. 
Acanthocyclus gayi, Milne Edwards and Lucas. 
Acanthocyclus gayi, Milne Edwards and Lucas, Crust, in d’Orbigny, Voy. dans l’Amerique 
Meridionale, vol. vi. p. 30, pi. xv. fig. 1, 1843. 
„ ,, Miers, Proc. Zool. Soc. Lond., p. 69, 1881, and references to literature. 
A male and also an adult female of extraordinary size were taken at Valparaiso on 
the beach, and a small male in Messier Channel, Patagonia, in January 1876 (in fresh 
water). 
The dimensions of the adult female are as follows : — 
Adult $ . 
Lines. 
Millims. 
Length of carapace, nearly ...... 
H* 
30-5 
Breadth of carapace, ...... 
15* 
33 
Length of larger chelipede when extended as far as its conformation 
will allow, ....... 
21* 
45-5 
Legion (?) III. COEYSTOIDEA. 
Corystiens, Milne Edwards, Hist. Nat. Crust., vol. ii. p. 139, 1837. 
Corystoidea, Dana (subtribe), U.S. Explor. Exped., vol. xiii., Crust., p. 297, 1852. 
The Corystoidea, which are placed by Milne Edwards between the Leucosiidse and 
Dorippidse at the end of the Brachyura, in the classification proposed by Dana constitute 
a distinct subtribe between the Cyclometopa and Catometopa, and are regarded by 
Dr. Claus 1 as a distinct family of the Cyclometopa, and placed by him between the 
Portunidse and Thelphusidse. This is perhaps their most natural position, As limited 
1 Grundzuge der Zoologie, p. 636, 1880, 
(ZOOL. CHALL. EXP. — PART XLIX. — 1886.) 
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