OCR Text |
Show 700 MR. W. A. CUNNINGTON ON A NEW [May 16, foreign growths is easily accounted for. It is, I understand, the largest individual that M r . Moore has ever seen, and from its soft texture it had clearly recently undergone ecdysis, becoming for the time free from encrusting organisms. Affinities.-That this Crab finds its nearest allies among the freshwater group of the Thelphusida3 there can, I think, be little doubt. Of the three sections into which Ortmann has subdivided the group 1, the Pseudothelphusinse and the Trichodactylinae may be at once dismissed, as differing most markedly in the character of their external maxillipeds. This excludes the N e w World forms, leaving only, in the section Thelphusinse, those typical of the Old World, though occurring also in Australia. The principal points of resemblance to, and difference from, the members of this group, which this Tanganyikan crab presents, may be conveniently stated in tabular form. Points of resemblance to the Thelphusinse 2:- (1) Presence of distinct post-frontal crest. (2) Conditions of sutures on carapace. (3) Form of external maxillipeds. (4) Character of chelipeds. (5) Spinuliferous condition of ambulatory dactyli. (6) Normal seven-jointed nature of abdomen. Points of difference from the Thelphusinae: - (1) Length of carapace more nearly equal to tbe breadth. (2) Carapace considerably less vaulted. (3) Antero-lateral margins relatively longer. (4) Greater breadth and less deflection of front, with larger size of orbits and eyes. (5) Second joint of antenna not distorted by deflexed front. (6) Spotted nature of test. Two genera only-Parathelphusa and Thelphusa-are included by Ortmann under the heading Thelphusinpe. Of these, Parathelphusa was originally supposed to be typically Indo-Malayan in distribution, but in 1887 A. Milne-Edwards 3 included under this heading several forms originally described as Thelphusa from the African continent. The genus Thelphusa is widely distributed over all part3 of the Old World. By the kindness of Prof. Jeffrey Bell, M.A., I have been permitted to examine the large number of specimens belonging to these two genera in the collection of the British Museum. Among them there are no forms which would seem to be closely allied to Limnothelphusa, but so far as general appearance goes the specimens of Parathelphusa certainly agree most nearly. The latter have a carapace more elongated in 1 Zool. Jahrb. (Abth. f. Syst.) Bd. vii. 1894, p. 487. 2 The term is here used as instituted by Ortmann, though in his scheme ot classification he does not refer to the genera Hydrothelphusa and Platy-thelphusa. J Ann. Sci. Nat. vii., Zool. t. 4. |