40J: PALAEONTOLOGY OF ILLINOIS. 



long and slender; anterior pair not chelate. Telson long, 

 tapering and horizontally flattened; stylets with first joint 

 very small, second double, and also flattened horizontally. 



This is another remarkable type, presenting, so far as can be determined, 

 even a more puzzling combination of characters than that we have described 

 under the name Acanthotehon. In the nature of its antennae, with their appa- 

 rently well developed basal scales, the structure of its caudal appendages, and 

 its long, slender legs, spread out on each side, for walking in an erect attitude ; 

 as well as in the depressed, slender form of its abdomen and thorax, it seems 

 to present decidedly the aspect of a Macrural Decapod. Yet, on a closer exami- 

 nation, we can see no traces of a carapace, the thorax being apparently divided 

 into seven segments, like those of the abdomen, and each provided with a pair 

 of legs, as in the Tetradecapoda. If we are not mistaken in these latter 

 characters, and we certainly believe we are not, it must show a most extraordi- 

 nary union of characters, which, amongst recent Crustacea, belong to different 

 primary divisions. From all that can be made out of its structure, we are 

 therefore inclined to view it as one of the " embryonic" or "comprehensive" 

 types, so often met with in various departments of palaeontology, and which 

 furnish the advocates of the Darwinian hypothesis with some of their strongest 

 arguments. 



For the present, this genus is placed, provisionally, along with the Tetrade- 

 capoda, though it cannot, we think, be included in any known family of that 

 division ; while if it should prove to be an embryonic or low type of the Deca- 

 poda, it may be even necessary to establish for its reception a division of more 

 than family importance. It is proper to remark here, however, that we have 

 not seen any one specimen showing the caudal appendages we have described, 

 united with the other characters of- the thoracic and cephalic members, men- 

 tioned above. One imperfect specimen shows the seven thoracic and five or 

 six of the abdominal segments, with their legs and natatory appendages, the 

 head, antennae, and apparently their basal scales; while another shows the 

 caudal appendages, and all of the thoracic and abdominal segments, very dis- 

 tinctly, without any of the other members. The general agreement, however, 

 of these specimens, in the parts preserved in each, is such that scarcely a doubt 

 can be entertained, that they belong to the same species. Yet, in order to pre- 

 vent confusion, we would remark, that in case they should prove to belong to 

 different genera, or species, that it is the form showing the head, antennae, tho- 

 racic and abdominal segments, with their appendages, &c, that we regard as 

 the type of the genus and species. 



