CHARLES W. HOOKER. 11 



The five tarsal joints vary only in length, the first being 

 nearly as long as the other four, the others, except possibly 

 the last, gradually decreasing in length beyond the first. At 

 the apex of the last tarsal segment is a pair of well developed 

 curved claws between which is a large pulvillus. On the 

 inner side of the claw between its base and apex are, except 

 in Retanzsia, several teeth (pectinate). In Ophion these are 

 rather fine, while in Thyreodon and Athyreodon they are 

 coarse. Aside from size, and the presence of two tibial 

 spurs instead of a cleaning apparatus, the posterior legs dif- 

 fer but little from the others. 



Abdomen (PI. I, figs. 2, 5). — The first true abdominal 

 segment is the median segment, propodeum or, as I have 

 called it following other writers, the metathorax ; this has 

 already been described under the thorax. Aside from this 

 the abdomen consists of seven visible segments, with a pos- 

 sibility that in the male the seventh is really the seventh 

 and eighth fused. It is long, falcate and usually strongly 

 compressed laterally except in Ophion biioveolatus and the 

 Genus Retanisia. The first two segments are usually some- 

 what cylindrical, and slightly enlarged at the distal ends ; 

 beyond this the abdomen is enlarged more or less acutely, 

 depending on the genus and species. In Ophiopterus it is 

 narrow throughout while in most of the other genera it is 

 enlarged beyond the second segment. At the apex are the 

 two short, clavate cerci often seen in other Hymenoptera. 

 In the female the apex of the abdomen is abruptly truncate 

 and from its lower edge projects the ovipositor, with its base 

 hidden in a groove and its apex protected by a short sheath. 

 In most of the genera it is short and stout, but in Ophiop- 

 terus it is longer and more slender. 



In the male the apex of the abdomen is more gradually 

 narrowed and with two subtriangular clasps below. Differ- 

 ence in the shape of these has been given specific value by 

 some, but this seems questionable. Between these and 

 sometimes projecting below them is the short, stout penis. 



Sexual distinctions. — Aside from the presence of an ovi- 



TRANS. AM. KNT. SOC, XXXVIII. 



