30 
MEMOIRS OP 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 geuus (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 Caecidotaea to Ccecasellus, but defer to the present 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 aud 
relations were misunderstood, and it was made the type of a new genus ( (Jacidotwa Packard). It was soon redescribed 
by Professor Cope, under the specific name microcephalus; 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 Crustacds d’eau douce 
de Norvfege, has failed to reveal any structural peculiarities which could positively serve as the characters of a distinct 
genus, aud I have therefore united it to Asellus (p. 11). 
It remains to be seen, however, whether Mr. Porbes has not somewhat overstated the case, 
aud 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 Cceci 
dotcea stygia and Ccccidotcea 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 
Cuecidotsea 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 Osecidotsea 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 acccompanied by other 
changes iu form and structure; and so with other oases. 
If we turn to the European Asellus forelii Blanc, a blind species from the abysses of Lake 
Leman (for specimens of which we are indebted to the kindness of Professor Forel), we see that 
it does not belong to our genus Caecidotaea; although it has been referred to Caecidotaea by Fuchs 
in his paper on the fauna of the deep sea. Asellus forelii , compared with specimens of Asellus 
aquations from Belgium (obligingly sent us by Prof. E. Yan 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. cavaticus Schiodte, 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 Ccccidotcea 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 Cascidotsea. 
* See 5th Rep., Peab. Acad. Sc., Salem, 95,1873, 
