DECAPOD CEUSTACEANS OP THE OXFOED CLAY. 555 



allied to M. hrevimanus, Miinst. (Solenhofen), but that species is 

 a third larger, and the figure in Oppel (Pal. Mitth. tab. xxii. f. 5) 

 appears to indicate three lateral cephalic ridges ; and the propodite, 

 in contradiction of its specific name, is relatively longer than in 

 M. socialis. M. Pearcei, M^Coy, is twice or three times as large, 

 and I fully concur with Dr. Woodward in regarding it as a 

 distinct species. 



GONIOCHIETJS CKISTATTJS, UOV. sp. (PI. XVI. fig. 9,) 



Chelae short, robust, basal portion of propodite (hand) wider than 

 long ; dorsal surface slightly more convex than the palmar ; border 

 corresponding with the fixed finger rounded, bearing tubercles, a few 

 of which are scattered over the adjacent portion of both the palmar and 

 dorsal surfaces ; the border corresponding w^ith the daetylopodite has 

 a tuberculated " carinal expansion " (Etallon), subtended on each side 

 by a narrow, longitudinal furrow ; articular cavity for daetylopodite 

 large, occupying more than half the distal extr^emity of the hand ; 

 carpal articulation large, very oblique. Pingers varying in length 

 from a third to half the length of the hand, both deflected towards 

 the palmar plane ; outer border of both fingers flattened, and bearing 

 a series of numerous, crowded, conical tubercles of various sizes ; 

 dentary border widening from apex to base, and bearing a row of 

 6-9 crushing-tubercles near the dorsal edge; palmar and dorsal 

 surfaces of both fingers flattened, smooth (or with a few palmar 

 tubercles), and impressed by large, oval pits for capillary tufts. 



I refer these chelae to a species of Goniochirus rather than to a 

 form of the nearly allied genus Orhomalus, Etallon, by reason of the 

 large size of the articulation for the daetylopodite, the great obliquity 

 of the carpal articulation, as also the carinal expansion on the 

 border corresponding to the daetylopodite, and the equal degree 

 of convexity of the palmar and the dorsal surfaces of the hand, 

 M. Etallon describes the palmar surface in Orhomalus as bein^' 

 flattened and capable of close apposition to the under surface of the 

 carapace, as in the Cryptopods. The specific name applies to the 

 crowded crest of tubercles on the outer borders of the fingers ; 

 this character will distinguish this from the only other described 

 species — G. Baheaui, Etal., and G. Jaccardi, Etal. The onl}' por- 

 tions which I have been able to identify are the choice ; these occur 

 abundantly, but vary considerably in form and size. 



Length of hand from carpal base to finger-tip from 20 to 30 millim. ; 

 width of hand from 15 to 25 millim. 



Oxford Clay, St. Ives. 



Coll. Woodwardian, Newcastle, Oxford, Mr. George, and my o\vn. 



Specimens numerous. 



M. Etallon classifies the genus Goniochirus among the Brachyura, 

 but suggests the probability that it may be proved, by the discovery 

 of other portions, to be an Anomurous form. If it should be definitely 

 determined to be a true Brachyuran, it would acquire considerable 

 interest as being one of the earliest representatives of that class. 



In general form these chelae resemble those of two Cretaceous 



