200 



ö 



such a character ^) : the genus Typhlocarcinops^ except for this slight difference, is absolutely 

 and intimately related to Typhlocarcinus Stimpson, as regards all principal features. Personally 

 I am convinced, that there is no need of such a sharp demarcation between the two genera, 

 as to range them in different subfamilies, and I think it is preferable to include TypJilocarcinops 

 into the Rhizopinae by a slight modification of the diagnosis of the latter. 



The lack of sculpture and the absence of dentation of the carapace, together with the 

 great uniformity in the shape of the small, sharply-keeled chelae, renders the discrimination of 

 the species, and even in some cases of the genera, a rather troublesome undertaking. Alcock 

 has admirably succeeded in drawing up a synoptical key to the genera known to him, from 

 British Indian waters, and it is his key, which is here largely used, with addition of all Indo- 

 Pacific genera, that I know of. 



Almost all the Rhizopinae are of small size, a few millimetres in breadth, and the 

 majority seems to seek shelter in coral stocks, worm tubes etc. ; it is to this habit, that the 

 general reduction of the eyes, going even to complete blindness, is to be attributed. Most of 

 the species are living in rather shallow water, but a few genera are obtainable from rather 

 considerable depths (400 — 500 fathoms). 



Key to the genera : 



1. Antennules completely fit into the fossae beneath the front .2 

 Antennules cannot be folded up (so as to be concealed in 



dorsal view of the animal), as the basal joint entirely fills 

 the fossa 14 



2. Epistome of good length, commonly prominent at posterior 



margin 3 



Epistome short, not prominent at posterior margin . . . . 13 



3. Eyes well formed, nearly always pigmented 4 



Eyes obsolete, or nearly so ; if distinct, the first abdominal 



segment of both sexes occupies the whole breadth of the 

 last sternal segment 9 



4. Eye-stalks movable, not fixed into the orbits 5 



Eye-stalks firmly fixed and completely filling the orbits. Antero- 



lateral angle of merus of external maxillipeds conspicuously 



produced outward Ceratoplax Stimpson 



5. Carapace smooth, glossy, lateral margins parallel, fronto-orbital 



breadth nearly equal to greatest width of carapace. Walking 



legs elongate, much longer than breadth of carapace . . Notonyx A. ÏNIilne-Edwards 

 Lateral margins of carapace never parallel, fronto-orbital breadth 

 generally not exceeding half the greatest width of the cara- 

 pace, usually narrower 6 



6. Lateral margins of carapace divergent backward, front narrow. 



l) Even within the liraits of a single genus (f. i. Goneplax) the breadth of the abdomen may vaiy in this respect, that the third 

 segment either touches, or does not reach, the coxopodites of the penultimate pair of legs. 



52 



