214: Prof. J. R. Henderson on a 



the two sexes have thus simultaneously undergone modifica- 

 tion in different directions, the general appearance ot' the 

 male suggests that he is less nio litied thau the female, and 

 consequently any attempt to determine the relationships of 

 the anomalous family HapalocareiuidiE will probably have to 

 be based largely on the characters of the male. 



]n more than one account these crabs have somewhat 

 loosely been referred to as parasites on the living corals, 

 ■whereas there is no reason to suppose that the condition is 

 one other than that of eoramensalism. There is nothing to 

 indicate that they obtain any part of their nutriment at the 

 expense of the coral colony, though doubtless the crab 

 deprives the polyps of many food-particles which would 

 otherwise have fallen to their portion. Stimpson's sugges- 

 tion that Hapalocarcinus feeds upon the coral polyps is 

 negatived by the observation of Semper that colourless 

 })olyps exist on the inner surface of the " gall." 



Family Hapalocarcinidas. 



Cryptochirus dimorphus, sp. n. (PI. YIII.) 



Characters of the female. — The carapace is elongated and 

 ])ractically four-sided, with the length less than twice the 

 breadth ; the surface is everywhere roughened by short 

 acute spinules with rather broad bases, which are more 

 crowded together posteriorly, but somewhat reduced in size 

 near the hind margin ; in some cases on the posterior fourth 

 or so of the carapace the spinules are represented by small 

 crowded granules. The regions of the carapace are not de- 

 fined, and the surface is practically level, with the exception 

 that the gastric region is sometimes slightly circumscribed, 

 and a slight hollow on either side, in which the spinules are 

 comparatively few, separates it from the hepatic regions. 

 The carapace is sliglitly convex from side to side and 

 distinctly convex from end to end ; when the crab is viewed 

 from the lateral aspect, the greatest height is seen about the 

 middle of the branchial regions or a little behind the middle 

 of the carapace. The anterior or frontal margin has four 

 subequal, equidistant, rounded, spinule-capped lobes ; the 

 two submedian or, properly speaking, frontal lobes project 

 forw^ards to a slightly greater extent than the other pair 

 situated at the antero-latcral angles of the carapace. The 

 amount of projection of the four lobes, or, to state the same 

 fact in another way, the extent of the three intervening 

 indentations, vanes ni ditl'erent individuals; in most cases 



