208 
THE YOYAGE OF H.M.S. CHALLENGER. 
The principal dimensions of this specimen are as follows : — 
Adult . Lines. Millims. 
Length of carapace, . . . . . . . 221,- 47 
Breadth of carapace to base of antero-lateral marginal spines, . 43 91 
Legion II. CYCLINEA. 
Cyclinea, Dana, U.S. Explor. Expect, vol. xiii., Crust. 1, p. 294, 1852. 
This section was established by Dana for the single genus Acanthocyclus, which is 
intermediate in structure and position between the typical Cancroidea, the Plagusiinae, 
and, as pointed out by Dr. Strahl , 1 the genera Bellia and Corystoides, which in Dana’s 
system constitute a distinct subtribe, Bellidea, of the Crustacea Anomura. The nearest 
ally to Acanthocyclus is, I think, Bellia, which resembles Acanthocyclus in the more or 
less orbiculate carapace, in the form of the front, chelipedes, and ambulatory legs, but is 
distinguished by the narrower, more elongated merus of the exterior maxillipedes, by the 
broader post-abdomen of the male, and the less distinctly defined buccal cavity. Perhaps, 
nevertheless, as in Dr. Strahl’s arrangement, this genus should be placed in the same 
section of the Brachyura as Acanthocyclus. 
The Cancroid genus Cymo, and the genus Crossotonotus, which is placed by A. Milne 
Edwards in the Catometopa (which have a more or less orbiculate carapace) are 
distinguished from Acanthocyclus by the form of the front, the well-developed flagellum 
of the antennae, &c. 
Acanthocyclus, Milne Edwards and Lucas. 
Acanthocyclus, Milne Edwards and Lucas, Crust, in d’Orbigny, Voy. dans l’Amerique, 
Meridionale, Zool., voL vi. p. 29, 1843. 
Plagusetis, Heller, Verhandl. d. k. k. zool.-bot. Gesellscb. Wien, vol. xii. p. 522, 1862. 
In this genus the carapace is subcircular, moderately convex, with the cervical and 
cardiac-branchial sutures distinct, the lateral margins are arcuated, or, in adult examples 
of large size, the carapace is somewhat quadrate, with the angles rounded. The antero- 
lateral margins are dentated. The front is rather narrow, with a prominent median lobe, 
which projects considerably beyond the interior angles of the orbits, which are small 
and without fissures. The post-abdomen (in the male) is narrow and five-jointed, with 
the third to the fifth segments consolidated. The epistoma is very small. No longi- 
tudinal ridges are developed upon the endostome. The eye-peduncles are short. The 
antennulary fossse are very small, and receive no more than the bases of the antennules. 
The basal antennal joint is short, moderately dilated, and fills the interior orbital hiatus ; 
1 Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 714, fig., 1861. 
