74 EDUAKD UHLENHUTH. 



and which furnish valuable suggestions as to the methods which 

 must be employed in order to procure a large number of animals. 

 The writer hopes to stimulate a search for these salamanders on 

 a large scale, in order to make this interesting form accessible to 

 the experimental biologist who is in need of just such an animal 

 as Typhlomolge rathbuni for attacking many important problems. 



GENERAL CHARACTERS OF THE REGION. 



As pointed out, the specimens described first by Stejneger were 

 found in the basin of the Artesian Well in the Fish Hatchery in 

 San Marcos, and were carried up into this basin by the flowing 

 water of the Artesian Well. During a two months' stay in San 

 Marcos, we secured only two specimens from this basin, but five 

 other specimens were found in three other localities, i.e., in Frank 

 Johnson's Well, in Ezell's Cave and in Beaver Cave. 



In order to understand the conditions which might have led to 

 the present distribution of Typhlomolge and because these con- 

 ditions in the future may be an important guide in tracing the 

 subterranean channels which the animals inhabit, a careful study 

 was undertaken. It was found that the conditions in the three 

 places where we found Typhlomolge are essentially similar to 

 those existing in the locality from which the water of the San 

 Marcos Artesian Well is derived. 



Before describing the well and the caves in which we found 

 Typhlomolge it is necessary to point out the geologic peculiarities 

 of this area of Texas, since these conditions not only led to the 

 formation of the caves but also to the present distribution of the 

 Typhlomolge. Whether or not they are also responsible for the 

 peculiar characteristics of the animal as Eigenmann and Stej- 

 neger assume, is an important question, the answer to which, 

 however, cannot be given before extensive experiments on this 

 species have been carried out. 



San Marcos is located on the so-called Balcones scarp line. 

 This line runs from Austin to Del Rio in a south-westerly direc- 

 tion and separates in a most distinct way the Edwards Plateau 

 (north of the line) from the Rio Grande Plain (south of the 

 line). It forms the escarpments of the plateau towards the plains. 

 Along this line a faulting has taken place in Eocene time (Hill 



