460 bulletin: musel"tm of comparative zoology. 



52. Plethodon dorsalis (Cope). 



Kt.: Bee Spring, 2,222; 4,703; Glasgow Junction, 1,885; Mammoth Cave, 

 1,681 (27). 



Plethodon dorsalis differs from Pldhodon cinereus in the following- 

 characters : — 



1. There is usually one less costal groove. 



In P. cinereus the greatest possible count of costal grooves is twenty. 

 This is obtained by counting as the first one, one immediately over 

 the arm, and as the last, a forked one immediately in front of the 

 leg. If, as sometimes happens, the one over the arm is missing, and 

 the one in front of the leg is not forked, there would be eighteen 

 grooves. Very rarely there is a more real variation, in that one of the 

 middle grooves is lacking. In this case a count of all the grooves 

 would give nineteen and a count omitting the end grooves as before 

 would give seventeen. Now in P. dorsalis, counts exactly similar to 

 those given above for P. cinereus, give nineteen as the maximum num- 

 ber, which would be seventeen, if, as is usually the case in this form, the 

 one over the arm and the fork of the last groove are both missing; 

 but only rarely does the count rise so high, for in at least half the 

 series the maximum count gives only eighteen and in these specimens 

 a minimum count (and this minimum count is more accurate in P. 

 dorsalis than in P. cinereus) gives only sixteen. To sum up, if we 

 omit one groove sometimes present over the arm (much more fre- 

 quently in P. cinereus) and do not as a separate groove a fork of the 

 one just in front of the leg (and this also is more frequent in P. cine- 

 reus), the costal grooves of P. cinereus are eighteen, rarely seventeen, 

 and those of P. dorsalis are indifferently seventeen or sixteen. 



2. The tail of P. cinereus is longer than that of P. dorsalis. In 

 P. dorsalis the tail is never as long as the head and body, while in 

 P. cinereus it is often longer. 



3. The dorsal band or strip is in all but one of this series markedly 

 zigzag, so that the stripe resembles that of Desmognathus ochrophaea 

 carolinensis. In one of the series the stripe is straight edged, but 

 much narrower than that of P. cinereus of equal size. This specimen 

 has a head-and-body length of 40 mm. The stripe is between 1 and 

 2 mm. wide. In P. cinereus of the same size from Massachusetts the 

 stripe is over 3 mm. wide. 



Like P. cinereus this form has a melanistic phase. It is, however, 

 much rarer and seems to be a gradual darkening with age rather than 

 a true melanistic variety. Four of the thirty specimens in the col- 



