2 University of Michigan 



the preserxing fluid. These were soon seen-to be parasites and 

 were saved. A very brief preliminary study showed that they 

 were larval trematodes or cercaria. The collectors further 

 noted that all these snakes with the swollen tails came from a 

 short part of Alusquiz Creek, a small stream flowing through 

 ^[usquiz canyon. At this time it was thought that none of the 

 specimens of the two species of Thamnophis occurring in 

 neighboring localities were infested with this parasite and thus 

 a problem in local distribution of the parasite was presented. 



Upon the return of the expedition the writer was given the 

 opportimity to examine all of the snakes of these two species 

 caught diu-ing the summer, and a superficial examination of 

 thirteen other specimens of T. marciana and of two specimens 

 of T. cqucs wliich had been collected along Limpia Creek and 

 about artificial ponds at Fort Davis and the surrounding coun- 

 try revealed no external appearance of parasites. A careful 

 internal examination showed, however, that two of the three 

 specimens of T. marciana caught in the village of Fort Davis 

 were infested with small numbers of this parasite and one of 

 the two was parasitized with small numbers of another cer- 

 caria. Of the three specimens of T. marciana from Limpia 

 canyon none were parasitized while one of the two T. cqucs 

 from Limpia canyon was infested with a few of the second 

 form of cercaria. There is then nothing remarkable about the 

 local distribiUion of this parasite. Apparently the snakes 

 about Musqtiiz Creek had more abundant opportunity for 

 infestation than snakes from other creeks and ponds in the 

 region of Fort Davis, or from Limpia canyon. 



In appearance the tails of the heavily parasitized snakes are 

 worthy of note. The tails are swollen ; the scutes more or 

 less erect thus giving the tails a roughened appearance. In 

 three instances a large portion of the tail had been lost. 



