BIHANG TILL K. sv. VET.-AKAD. HANDL. BAND 20. AFD. IV. NtO 1. 11 



between Camharus Clarkii and C. acherontis. At the first 

 glance at Hagen's (2) (Pl. IV) figure of the former they seem 

 very difFerent as C. Clarkii is so v.ery mucli the larger and 

 robuster, but a earefnl examination will give a different result. 

 Before we discuss the likeness however, it seems advisable to 

 see what characteristics the varieties of the blind crayfishes 

 have in common. In this way possibly the direction or ten- 

 dency of transmntation can be nnderstood. We shall find 

 then that all the blind forms are smaller and more slenderly 

 built. The chelcB are not so broad as on the normal-eyed 

 forms, but rather subcylindrical. The first character probably 

 is dne to the fact that food is more scarce in the caves. The 

 absence of light makes the functioh of the eyes superfluous, 

 and thus they are rednced throngh not being nsed. As the 

 crayfishes in the caves do not have so many enemies, they 

 need not to be so strongly armed with spines and tubercles. If 

 we now make the snpposition that a specimen of Cambarus 

 Clarkii were rednced in the way snggested above, I think we 

 should get something rather similar to Cambarus acherontis. 

 The broad rostrum with only slightly developed lateral 

 teeth which are to be regarded as the ends of the lateral 

 crests, the tuberculated surface of the carapax, the absence 

 of spines, the narrow areola. the broad and short terminal 

 lamina of the telson, the ec^uality in length of the abdomen 

 and the cephalothorax ' are all characteristics the both have 

 in common. The tubercle on the basal joint of the fourth 

 pair of the legs and the smaller one on the basal segment of 

 the fifth pair of the legs are essential features too of both 

 species. Regarding the difPerent size the male appendages of 

 the first abdominal segment are similar in both species too. 

 As a result of this comparison I think it seems very probable 

 that the ancestors of Cambarus acherontis were if not exactly 

 members of the present species of C. Clarkii so at least some- 

 thing rather similar to the same. The geographical distribu- 

 tion of that species is not without value in this question 

 either. It is more widely distributed than the other two 

 Florida species and is therefore probably older than any of 

 them and more primitive and thus more likely to represent 

 the ancestors of Cambarus acherontis than C. Alleni and 

 fallax which have never lieen found outside the State of 

 ' C. Alleni and fallax have abdomen longer than cephalothorax. 



