34 astacid^:. 



the other groups. Some, no doubt, will prefer to regard C. pellucidas as 

 a distinct group or genus, still, as I am convinced, without foundation. 

 The most striking differences consist in the aberrations in the shape of 

 the fore parts and of the limbs of the head. But it seems to be a some- 

 what well-recognized law in nature (Rathke, Metamorph. Retrograd., 

 p. 125) that if any part is atrophied, or stopped in development, the 

 nearest parts show an abnormal increase of development. This is 

 apparently the case in C. pettucidus ; the eyes are atrophied, and the 

 rostrum, the fore border of the cephalothorax, the antennal lamina, 

 the basal joint of the inner antennas, and the epistoma are altered 

 or largely developed. 



Similar alterations are not rarely noticed in the insects. The blind sol- 

 diers of Termes have the head and the mandibles more developed, the 

 maxillae and the labium atrophied. Analogous facts are observed in the 

 ants and in the two very nearly related Coleopterous species, Ht/lccoetus 

 dermestoides and flabellicornis. In H. dermestoides the antennas are simple, 

 the maxillary palpi extraordinarily developed ; in H. flabellicornis the 

 antennas are much developed and the maxillary palpi simple. It would 

 not be difficult to give a greater number of similar examples. 



The two species of the third section are not as abnormal as C. pel- 

 lucidus, and they differ only in the two characters before mentioned. 



Synopsis of the Species. 



1st Section. (See p. 33.) 



a. Epistoma rounded in front : C. acutus, C. Blandingii. 



b. Epistoma truncated in front : C. Clarkii, C. troglodytes. 



2d Section. (See p. 33.) 



a. Areola narrow : C. fallax, C. LeContei. 



b. Areola broad : G. spiculifer, C. angustatus, C. versutus. 

 (IncertJe sedis.) : C. maniculatus. 



3d Section. (See p. 33.) 

 C. penicillatus : C. Wiegrnanni. 



4th Section. (See p. 33.) 

 C. pellucidus. 



