82 ASTACID^. 



pedes quartos laevi, annulo transverso inflato, apertura media profunda * 

 transversal! ; postabdomine latiori, basi summa angustiori. 



(Maxim.) Long. corp. 4.5; antenn. 2.6; ped. antic. 4. 



Habitat : Evanston, Lawn Bidge, and Belleville, Illinois, and the 

 prairies near Chicago (Philad. Acad.) ; Petersburg, Va. ; Monticello, 

 Miss. ; Arkansas ; New Orleans ; Kelley's Island, Ohio ; Lake Erie ; Lake 

 Michigan ; Garrison Creek ; Sackett's Harbor ; Lake Ontario. 



Vidi 16 specimina. The Salem Museum contains a full-grown male 

 and a very young male of the second form, the abdominal legs not 

 being articulated. 



C. ohesus is very similar to C. latimanus, but the " areola nulla " always 

 separates them instantly. The thorax is more ovoid than in 0. latimanus. 

 The epistoma is not pointed anteriorly, the second joint of the external 

 antennas has no spine ; the carinas are posteriorly calloso-inflataB. 



One female (Garrison Creek, Philad. Acad.) was labelled C. propin- 

 quns ? but the type of 0. propinquns, communicated by Professor Stimp- 

 son, is a different species. 



I have not seen the C. diogenes Girard. Although he treated of it 

 at some length, he left it without an accurate description. The dorsal 

 lines of the carapace are almost contiguous, so that the areola is almost 

 wanting. I am in doubt whether it can be referred to G. obesus. The 

 only specimen, from Georgetown, D. C, in the Museum is C. Bartonii. 

 Perhaps C. Diogenes is also C. Bartonii. 



A specimen from the District of Columbia, labelled 0. Diogenes, in 

 the Museum of the Philad. Acad., does not agree at all with the descrip- 

 tion of Mr. Girard, and is C. propinquns. 



A single female from New Orleans differs in having a narrower ros- 

 trum, with the margins parallel and the tip more acute. The first pair 

 of abdominal legs, ordinarily bearded at the margins and flattened, are 

 singularly transformed. They are thicker, cylindrical, with the tip 

 narrower and twisted, as is the case with the abdominal legs of Astacus 

 fluviatilis. The postabdomen is narrower at the base. Possibly this 

 specimen is a sterile female. 



Another female, in shape and size similar to the foregoing (3.2 inch, 

 long) has the rostrum broader, the margins not so much thickened as 

 in the type, the acumen more acute. The hand is more flattened and 

 not so strongly dotted, the inner margin more rounded, with six strong 

 and separated teeth, giving to the specimen a very peculiar aspect. 

 The two anterior spines of the inner margin of the carpus are long and 

 more developed. The annulus between the fourth pair of legs has its 

 anterior margin irregularly tuberculated. The right hand is wanting ; 

 I regard the specimen as abnormal and deformed. 



Cat. No. 165, Belleville, 111., Dr. Engelmann. Fern. Spec. 2. 



Cat. No. 1461, Evanston, 111. Male. Spec. 1. 



