282 A. Alcock — Garcinological Fauna of India. [No. 3, 



of considerable length. The buccal orifice is typically, but by no 

 means always, square cut. 



The palp of the external maxillipeds usually articulates either at 

 the summit, or at or near the external angle, of the merus ; but often, 

 as in almost the whole family Gonoplacidse, it articulates distinctly at 

 the antero-internal angle. 



The genital ducts of the male usually perforate the sternum opposite 

 the last pair of legs : if, as happens in the family Gonoplacidse, they 

 perforate the bases of the last pair of legs, they pass forwards to their 

 destination in a groove in the sternum. 



The abdomen of the male is very often narrow at its base and so 

 does not cover all the space between the last pair of legs. 



The branchiae are often fewer than 9 — from 8 to 6— on either side : 

 their efferent channels open on either side of the palate. 



The Catometopa may be divided into 9 families. One of these, the 

 Gonoplacidse, so closely approaches the Cyclometope family Xanthidse 

 that such Xanthoid forms as Geryon and Oamptoplax have by some 

 authors been included in it, while, on the other hand, some of its consti- 

 tuent genera, such as Gonoplax and Garcinoplax, have been ranged among 

 the Cyclometopes. 



Three other families, namely, the Grapsidse, the Geocarcinidse, aud 

 the Ocypodidse, include the typical Catometopes, upon which our general 

 conception of the group is founded. 



The remaining five families are more or less aberrant, they are the 

 Pinnoteridse, the Mictyridse, the Hymenosomidse, the Palicidse, and the 

 Ptenoplacidse. 



Of these aberrant families, the Pinnoteridse are probably most nearly 

 related to the Gonoplacidse, the Mictyridse to the Ocypodidse, and the 

 Palieidse to the Grapsidse, 



The true position of the Hymenosomidse appears to me to be still 

 doubtful. Many authors place them near the Pinnoteridse and Mictyridse, 

 and T think that their most natural place is alongside the Mictyridse. 

 Ortmann alone boldly removes them from the Catometope grade al- 

 together and unites them with the Oxyrhynchs, which I think is a 

 decided mistake. 



There remains the family Ptenoplacidse, which includes the single 

 species Ptenoplax notopus. This, though it has a superficial resemblance 

 to Macrophthalmus, is remote from that genus in many important cha- 

 racters, and, though it has no look of Hexapus, yet shows an attraction 

 to Hexapus and Lambdophallus that can hardly be accidental. 



