THE CANCROID CRABS OF AMERICA 



171 



Genus ACANTHOCYCLUS Milne Edwards and Lucas 



Acanthocyclus Milne Edwards and Lucas, d'Orbigny's Voy. TAmer. Merid., 

 vol. 6, pt. 1, 1844, p. 29; type, A. gayi Milne Edwards and Lucas. 



Plagusetes Heller, Verb. k. k. zool.--bot. Ges. Wien, vol. 12, pt. 1, 1862, p. 522 

 [4]; type, P. elalus Heller. 



Carapace slightly broader than long, rotund, sides dentate, teeth 

 extending a little way on the posterolateral margin. Orbit small; 

 eye short, peduncle stout. Pterygostomian region not prominent. 

 Front heavily margined, teeth rounded, median tooth much larger 

 than lateral. The antennae terminate with the basal article. Merus 

 of outer maxilliped subcircular, with a very shallow distal emar- 

 gination. Chelipeds stout, very unequal. Dactyli of legs curved, 

 acuminate. Male abdomen small, narrow. 



Three species inhabit the South American coast, so nearly related 

 that they may easily be mistaken for one another. The differences 

 are arranged below in tabular form as most convenient for quick 

 determination. 



Characteristics of the species of Acanthocyclus 



A. gijiji 



A. albatrossis 



A. hassleri 



Narrow; width l.O.i to 1.08 times 

 length. 



Lateral teeth intermediate 



Front entire 



Dactyli of ambulatory legs short, 

 much curved from base. 



End of basal antennal article 

 swollen in a wide, smooth, 

 round protuberance curving, 

 over on to the front. 



Abdomen of male narrow; sides of 

 fourth, fifth, and sixth segments 

 subparallel. 



Both carapace and legs very hairy. 



Carapace almost smooth 



Ischium joints of ma-\illipeds with 

 inner margins subparallel, but 

 leaving a wide hiatus. 

 Merus joints of ma.'iillipeds with 

 their outer margins subparallel 

 and continuous with the outer 

 margins of the ischium joints. 

 Orbit viewed from above less than 

 twice as wide as deep. 



Width intermediate, 1.08 to 1.13 

 times length. 



Teeth prominent, acute 



Front faintly bilobed 



Dactyli long, little curved 



.\ntennal article not swollen at the 

 very end, but furnished with a 

 blunt, projecting tooth, between 

 which and the front a narrow 

 furrow runs. 



Abdomen wide; sides of the sixth 

 segment convex, of fifth concave, 

 of third and fourth converging 

 distally. 



Less hairy -._ 



Carapace tuberculate or granulate. 



Ischimn joints with inner margins 

 in contact. 



Merus joints divergent, i. e., their 

 outer margins make quite an 

 angle with the outer margin of 

 the ischium joint. 



Orbit viewed from above less than 

 twice as wide as deep. 



Wide; width 1.16 times length. 



Teeth appressed. 



Front entire. 



Dactyli short, much curved. 



Antennal article as in albatrossis 



Abdomen intermediate; sides of 

 the sixth segment convex, of 

 fifth straight, of third and 

 fourth converging distally. 



Less hairy. 



Carapace tuberculate. 



Ischiunr joints with inner mar- 

 gins diverging anteriorly; gape 

 less than in gayi. 



Merus joints similar to those of 

 gayi. 



Orbit viewed from above more 

 than twice as wide as deep. 



ACANTHOCYCLUS GAYI Milne Edwards and Lucas 



Plate 75; Plate 76, Figure 4 

 Acanthocyclus gayi Milne Edwards and Lucas, d'Orbigny's Voj'. I'Amer. 

 Merid., vol. 6, pt. 1, 1844, p. 30; atlas, vol. 9, 1847, pi. 15, fig. 1-1/ (type- 

 locality, coasts of Valparaiso; cotype in Paris Mus., and in Mus. Phila. 

 Acad. Sci.). — Nicolet, in Gay's Hist. Chile, Zool., vol. 3, 1849, p. 176. — 

 Dana, U. S. Expl. Exped., vol. 13, Crust., pt. 1, 1852, p. 295; atlas, 1855, 

 pi. 18, figs. 4a-c. — Heller, Reise Fregatte Novara, vol. 2, pt. 3, Crust., 

 1865, p. 70. — ?CuNNiNGHAM, Trans. Linn. Soc. London, vol. 27, 1871, p. 494; 

 Lota. — Kingsley, Proc. Acad. Nat. Sci., Philadelphia, 1880, p. 37. — Rathbun, 

 Proc. U. S. Nat. Mus., vol. 21, 1898, p. 597.— Lenz, Zool. Jahrb., suppl. 

 5, vol. 2, 1902, p. 753; Tumbes, Talcahuano, Cavancha. 



