OP ARTS AND SCIENCES. 121 



single acute ante-apical spine on the superior margin, only one or two 

 distal spines in the outer row of biserial spines beneath. Third joint 

 of third pair of legs hooked. Fourth pair of legs with a conical tuber- 

 cle on the first segment. First pair of abdominal appendages short, 

 stout, twisted, distal half bent in towards the median line of the body ; 

 internal part truncate at apex, with a small spine directed backward 

 and outward ; external part longer, ending in a short, recurved, blunt, 

 laterally compressed, horny tooth. 

 Measurements : — 



Length of body 81 mm. 



" " cephalo-thorax 43.5 " 



" " abdomen . 37.5 " 



Length from tip of rostrum to cervical groove 27 " 



From cervical groove to posterior border of carapace ... 16 " 



Length of rostrum 11 " 



" " acumen of rostrum 5 " 



Width of base of acumen of rostrum 3 " 



, " " areola 3 " 



Length of antennae , 91 " 



" chela 36 " 



Width of chela , 15 " 



Length of movable finger 22 " 



One specimen, collected by Mr. F. W. Putnam in Green River near 

 the Mammoth Cave, Kentucky, November 3, 1874. 



This species is very distinct from every other known Crayfish. In 

 its general appearance it approaches those species included in the 

 group typified by G. Bartonii. The rostrum, however, is more after 

 the fashion of G. rusticus, but the lateral spines are much larger and 

 stand erect. The impressed external finger recalls G. robustus. The 

 sexual appendages are formed nearly as in G. Bartonii. The devel- 

 opment of the antennae is extraordinary. 



§ 4. Third pair of legs of male hooked. First pair of abdominal 

 appendages of male terminating in two elongated, straight tips. 



a. Rostrum without lateral teeth. 



12. C. medius, sp. nov. 



Male, form I. Rostrum of moderate length, excavated, slightly cari- 

 nated at the tip ; margins thickened, converging, sinuated near the tip 

 to form the short triangular acumen ; no lateral spines. Post-orbital 

 ridges depressed, sulcated on external face, subacute anteriorly. Cara- 



