30 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 



as in Asellus, while the middle joint of the mandibular palpus is not so large and thick, and there 

 are other differences, though of less importance. 



In our first notice of this genus ( Amer. Naturalist, v, 752) it was stated that it was closely allied 

 to Idotsea. This was a most unfortunate comparison, my observations having been based on imper- 

 fect specimens, which lacked the cercopods or anal stylets, and also the larger antennae. After 

 comparing it with Asellus communis the error was noted. * Under these circumstances I earnestly 

 desire to change the name Ceecidotaea to Ccecasellus, but defer to the j>resent rule of nomenclature, 

 that one author can not change a name based even on an unfortunate error. 



The present genus has not been regarded as a valid one by Mr. Forbes, who thus speaks of it 

 in his " List of Illinois Crustacea": 



This species has been peculiarly unfortunate. Described originally from an injured specimen, its structure and 

 relations were misunderstood, and it was made the type of a new genus (Ccecidotaa Packard). It was soon redescribed 

 by Professor Cope, under the specific name viicrocephalus ; and these imperfect descriptions have since been supple- 

 mented by several fragmentary notices in various papers by Packard and Smith. * * * A detailed comparison of 

 this species with undoubted Asellus, especially with the admirable plates of A. aquaticus in the Crustacea d'eau douce 

 de Norvege, has failed to reveal any structural peculiarities which could positively serve as the characters of a distinct 

 genus, and I have therefore united it to Asellus (p. 11). 



It remains to be seen, however, whether Mr. Forbes has not somewhat overstated the case, 

 and whether there are not a number of structural peculiarities which forbid our placing the two 

 known species in the genus Asellus. The more obvious and important of these have been already 

 noticed in the foregoing diagnosis of the genus. It should be observed that not only are Gceci- 

 dotcea stygia and Gcecidotcea nickajackensis without eyes, but that the body and appendages also 

 differ a good deal from any of the known species of Asellus. The genus seems as well founded as 

 many others in the Isopoda and other groups of Crustacea. We have little doubt but that 

 Csecidotsea has by modification and heredity been derived from Asellus, but because this is most 

 probable it is no reason why, from a systematic point of view, we should disregard its evident 

 generic characters; for it is now generally believed that somehow all the genera of Isopoda have 

 descended from some primitive form or genus. Because, then, we do know with some degree of 

 certainty that Csecidotaea has recently diverged from Asellus, and can see that the generic charac- 

 ters it possesses have been the result of its under-ground life, we should yet, from a purely taxo- 

 nomical point of view, regard it as a good genus. Of the genus Crangonyx some species are 

 blind and others are not, but the blind species do not present other important differences. It is 

 so with the species of Phalangodes, where the loss of eyes is not always acccompauied by other 

 changes in form and structure; and so with other cases. 



If we turn to the European Asellus forelii Blanc, a blind species from the abysses of Lake 

 Leman (for specimens of which we are iudebted to the kindness of Professor Forel), we see that 

 it does not belong to our genus Csecidotsea; although it has been referred to Csecidotaea by Fuchs 

 in his paper on the fauna of the deep sea. Asellus forelii, compared with specimens of Asellus 

 aquaticus from Belgium (obligingly sent us by Prof. E. Van Beneden), is about half as long and 

 broad as A. aquaticus ; the body has retained about the same proportions; the telson (abdomen) 

 is little if any narrower or more elongated. Both branches of the caudal stylets are of about the 

 same length as in A. aquaticus. Asellus forelii, then, appears to us to be evidently a depauperated 

 species, closely allied to A. aquaticus, which has lost its eyes by its life in supposed perpetual 

 darkness at or near the bottom of Lake Geneva. Its generic characters are identical with those 

 of its parent form, A. aquaticus. So also are those of A. eavaticus Sehiddte, found in wells in 

 Germany, and which closely resembles A. forelii, only differing in slight specific characters. It is 

 evident that these two blind species were originally derived from A. aquaticus, and hence have 

 retained the generic characters and specific marks of that European species as compared with our 

 American A. communis. 



When, however, we turn to our Cwcidotwa stygia and nickajackensis, we find that they are not 

 only not congeners of the blind European Aselli, but that they are also not congeneric with the 

 American Asellus communis, and that there are no intermediate forms connecting them, although 

 the eyed species of Asellus are somewhat variable. Hence we feel warranted, on taxonomic 

 grounds, whatever may be our theory about their origin, to retain the genus Cseeidotsea. 



* See 5th Rep., Peab. Acad. Sc, Salem, 95 } 1873, 



