286 ON THE NATURE OF EDESTUS AND RELATED FORMS. 



sake of comparison, we may briefly summarize the characters of the four genera in 

 question, arranged in the order of their progressive modifications, as follows: 



i. Campodus — Symphysial dentition consisting of a median azygous arched 

 series of fused teeth in one jaw, presumably the lower, opposed to which in (presum- 

 ably) the upper jaw is a paired series of corresponding teeth mutually separated, 

 and interlocking with the first. These series consist of at least thirteen greatly en- 

 larged teeth which are but little laterally compressed, whose coronal buttresses are 

 directed anteriorly, and whose crowns are inclined in the same direction, but without 

 being bent so as sensibly to override one another. Coronal apices very stout and 

 prominent, rather obtuse, their anterior and posterior margins sharp and smooth 

 or but faintly wrinkled. Lateral dentition consisting of about 20 transverse series 

 of Orodus-like teeth, arranged after the same general pattern as in Cestracion. Other 

 parts of the skeleton unknown. Carboniferous. Type, C. agassizianus de Koninck. 



2. Edestus — Symphysial dentition consisting of a moderately arched series 

 of fused teeth, which are fewer in number (5 to 8) than in the preceding genus, and 

 more laterally compressed. The segments are bent forward in such manner that 

 the base (corresponding to the enormously produced root) of each tooth ensheathes 

 those lying next in front. Coronal apices prominent, usually acuminate, and with 

 coarsely serrated anterior and posterior cutting margins, the latter more steeply 

 inclined than the former. Remainder of crown (corresponding to lateral extensions 

 of Campodus) greatly reduced. Lateral series and other parts of the skeleton un- 

 known. Upper Carboniferous. Type, E. vorax Leidy. 



3. Campyloprion — Symphysial dentition consisting of a strongly arched series 

 of fused teeth, which are relatively more numerous (14 to 20 or more) than in the pre- 

 ceding genera, higher-crowned, and more laterally compressed. Teeth reflected for- 

 ward so as to override one another toward their extremities, and fused for the greater 

 portion of their length. Coronal apices acuminate, finely serrated, and more closely 

 apposed to one another than in preceding genera. Series traversed by a median 

 longitudinal channel along the base, but without lateral grooves. Lateral series and 

 other parts of the skeleton unknown. Carboniferous. Type, C. lecontei Dean.* 



4. Helicoprion. — Symphysial series consisting of upwards of 150 fused teeth, 

 very similar to the last in form, but coiled into approximately 3^ whorls. Teeth 

 much compressed laterally, bent forward so as to override one another toward the 

 base, and traversed by a double lateral groove, as well as by a median longitudinal 

 channel along the base. Coronal apices acuminate, finely serrated along their an- 



* Substituted in place of C. annectans, which, according to Karpinsky (litt. 1902), approaches very closely the 

 type of Helicoprion. 



