244 iRiONYcniD^. 



present, I feel reluctant to admit species founded upon the modifi- 

 cation (and a modification assumed but in a comparatively late stage 

 of existence) of a sinji,lc organ, unaccompanied by any but correlative 

 differences ; and I maintain uuder the «ame species carnivorous as 

 well as conchifragous individuals. As before stated, similar varia- 

 tion is met with at distant points of the globe, and I have no doubt 

 that, as our knowledge progresses, other instances of this supposed 

 dimorphism wiU be brought to light. 



Synopsis of the Species. 



I. Costal plates eight pairs normally ; young with numerous 

 l()ngit\i(]inal dorsal dermal ridges or series of tubercles. — 

 Old World. 



A. All the costal plates separated 

 on the median line by the 

 neural plates ; head very large ; 

 postorbital arch extremely nar- 

 row, forming a keel on the 

 outer surface 1. suhplanus, p. 246. 



E, Last pair of costal plates in contact on the median line ; 

 postorbital arch expanded on the outer surface. 



1. Two neural plates between the first pair of costals ; 

 alveolar surface of lower jaw without a strong longi- 

 tudinal ridge at the symphysis. 



Inner edge of alveolar surface of man- 

 dible strong!}^ raised, forming a sharp 

 ridge, which sends off a short perpen- 

 dicular process at the symphysis ; inter- 

 orbital space, in the adult skull, nar- 

 rower than the external nasal opening ; 

 head with oblique black lines, con- 

 verging forwards ; no ocellar spots . . 2. gavgeticus, p. 248, 



Inner edge of alveolar surface of mandible 

 not or but very slightly raised, sym- 

 physis flat or with a longitudinal 

 furrow ; interorbital space narrower 

 than the external nasal opening ; head 

 with oblique black lines, converging 

 forwards ; young with small ocellar 

 dorsal spots 3. leithii, p. 249. 



Inner edge of alveolar surface of man- 

 dible not or but very slightly raised, 

 symphysis flat or with a longitudinal 

 furrow ; interorbital space, in the adult 

 skull, broader than the external nasal 

 opening ; head black marbled, with a 

 large yellow spot behind each eye ; 

 young with large ocellar dorsal sj)ots . 4. hurum, p. 249. 



