284 GEO. H. HORN, M. D. 



the eighth joint very short and narrower than the seventh or ninth. Last joint 

 of maxillary palpi longer than the third, cylindrical slightly acuminate at tip. 

 Prosternum short in front of the coxae, the cavities angulate externally and 

 closed behind. Mesosternum moderately separating the middle coxae and 

 oblique (vertical in obsoleta), and variably carinate (not carinate in ecarinaia). 

 Metasternum moderate in length, the posterior coxse contiguous. Abdomen 

 with six segments. Legs moderate, rarely long, short and rather stout in 

 obsoleta. Tibiae spinulose externally. Tarsi of moderate length, joints 5 — 5 — 4 

 in both sexes. Body oval or oblong. 



As above described Anisotoma is not strictly homogeneous there 

 being two species a little at variance with the others and one of them 

 especially so. A. obsoleta has the short robust form of Cyrtusa and a 

 vertical mesosternum between the coxae although not carinate in the 

 latter genus, here however the divergence from the typical structure 

 ends. On the other hand A. ecan'nata has the normal oblique meso- 

 sternum but there is no trace of carina, further the mandibles are 

 not toothed at the middle of the inner margin. There is however a 

 variability in the degree of carination of the mesosternum among the 

 other species, sometimes the carina is merely a raised line. I have 

 thought it better to admit these exceptional forms in the genus, rather 

 than separate them under names which would probably have but an 

 ephemeral existence. 



In number our species are much less than half those of Europe, 

 which fact suggests the possibility that a more careful search would 

 at least double our present number. 



The accompanying table will aid in distinguishing those at present 

 known to us. In it I have endeavored to avoid as far as possible the 

 use of sexual characters and have without their aid separated six 

 species, but the other seven have entirely refused to be separated 

 by any other means, and the resemblance is so great in several 

 cases that direct comparison without reference to the male might 

 prove deceptive. 



While all parts of our country have furnished specimens, the 

 species appear to have a wide distribution, at least this is shown 

 where a number of specimens have been examined. In several in- 

 stances one or two specimens only have been accessible and from 

 such a number no deductions can be made. We can however be 

 certain that at least four cross the continent and several others have 

 passed half that extent. 



In the table the arrangement seems to show a gradual transition 

 of the species from a resemblance to Hydnobius to a more certain 

 relationship to Cyrtusa. 



