616 PROCEEDINGS OF THE ACADEMY OF [Aug., 



The ^lanzaiiares Creek portercc represent a siibvariety having the 

 basal tooth with the outer denticle large and pointed, and the inner 

 one quite rudimentary, a mere slight swelling; umbilicus large, broadly 

 exposing penultimate whorl ; parietal tooth strong. On the other 

 hand, the Cooper's Mill thomsoniana have the basal tooth bifid as in 

 porterce, though they have the small size of typical thomsoniana. 

 Whether they should be regarded as another distinct subvariety is 

 uncertain, as' so few specimens of the Santa Fe Canon thomsoniana 

 have been collected. It is to be remarked that size is not connected 

 closely with altitude, regarding the whole series together. The large 

 porterce occupies the highest altitudes in the moimtains near Las Vegas. 



A single example from the debris of the Pecos river had no l^asal 

 or outer denticle, and could easily have been mistaken for A. ashmuni 

 (Dall). 



Dr. Grabham and I dissected a number of the Pecos cooperw, and 

 found the epiphallus with a basal curve and double insertion of penis- 

 retractor; spermatheca without any bulbous swelling at end, very 

 variable in length, that of seven specimens measuring respectively, in 

 mm., 29, 35, 22, 33.5, 35, 45, 31. 



In the Pleistocene beds at Pecos, AshmuneUa is represented by the 

 very distinct form I named pecosensis, but the other shells found in 

 the beds are identical wdth living forms, namely, Pyramidula cooperi, 

 W. G. Binney, P. cooperi depressa, Ckll.,* P. hemphilli, Newc, P. 

 shimekii, Pils.,* Succinea avara, Say,* Vitrea indentata umbilicata, 

 Singley,* Vallonia cyclophorella, Ancey, Pupa blandi, Morse, Limnaa 

 hiimilis, Say.* Those marked with an asterisk occurred only in 

 some dark-colored beds which seem to be more recent than the red 

 beds containing A. pecosensis. High up on the bluff Dr. Grabham 

 found an apparently fossil shell oi A. t. cooperce, more strongly ribbed 

 than the normal form, and thus tending toward pecosensis. 



