NATUEAL SCIENCES OF PHILADELPHIA. 



97 



species of the same genus. Thus in Spelerpes rubra they are entirely dis- 

 tinct at a very early period of larval life, while in S. cephalicus and S. 

 b e 1 1 i i, which much more nearly resemble the species of (Edipus in the dis- 

 position of the vomerine teeth and cylindric form of the tail, this separation 

 is much retarded. 



These genera may be parallelized also in the following manner, in illustra- 

 tion of the law of heterology :* 



Plethodontae. Spelerpese. 



A. one premaxillary. 



No fontanelle. 



Stereochila. 



Anaides, 



Batrachoseps. 



Hemidactylium. 

 Plethodon, 



A. fontanelle. 

 Toes 4—5. 

 Teeth large. 



Teeth small. 



Toes 4—4. 



AA. Two premaxillaries. 

 Toes free. 



Toes united. 



The minor relations may be more readily expressed thus : 



Plethodontae. 



Plethodon. 

 Anaides, 



Hemidactylium. 

 Batrachoseps. 



Or thus : 



two premaxillaries ; 



Oyrinophilus. 



Plethodon. 



Oeotriton. 



Hemidactylium. 



Digits 4 — 5, 

 Digits distinct. 



Two premax. 



One premax. 

 Digits united. 



Two premax. 



One premax. 

 Digits 4 — 4. 



Digits 4 — 5. 

 a. distinct. 

 Tongue free. 



Tongue attached. 



«*. united. 



Digits 4 — 4. 



Spelerpes. 

 Manculus. 



Gyrinophilus, 

 Geotriton. 



Spelerpeae. 



Gyrinophilus, . 

 Spelerpes. 



Oeotriton.. 

 (Edipus. 



Manculus. 



one premaxillary. 



Spelerpes. 

 Stereochila. 

 (Edipus. 



Manculus. 

 Batrachoseps. 



The above genera present, within restricted limits, not only the relations 

 which will be found to characterize genera elsewhere, but the relations between 

 all natural groups of whatever rank, or in other words, between groups defined 

 by structural peculiarities. From such simple cases we may derive the following 

 rationale of classification with reference to characters above the specific : First, 



1869.] 



•See origin of Genera, p. 53. 



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