132 Zoology of Colorado 



A curious little shell about 4 mm. across, discoid with a very 

 narrow aperture and practically flat upper surface, is the Micro- 

 physula ingersolli; named by Bland in 1876 in 

 recognition of the work of Ernest Ingersoll on 

 Colorado snails. It is quite common in the 

 mountains and is interesting because it represents 

 a group especially characteristic of Mexico and 

 Central America. It adds one more to the 

 numerous cases of southern types extending 

 northward, and meeting those (such as the 

 in^rsoffi h BulTd Punctum) of boreal distribution. 



(Enlarged) y^e f arn ily called Zonitidae consists of coiled 



shells, usually known by the smooth surface and simple margin 

 of the aperture, this margin being fairly or very ample, not nar- 

 rowed as in Microphysula. The one (Euconulus) in which the 

 aperture is rather narrow has a broadly conical spire or upper 

 portion, and is reddish brown. Like the Punctum, it is considered 

 a subspecies (E. fulvus alashfinsis) of a common European form. 

 Zonitoides arborea of Say is a very common species, about 5 mm. 



Euconulus fulvus alaskensia Pilsbry (Enlarged) Vitrina alaskana Dall 



across, with a very distinct umbilicus or opening beneath. The 

 name might be taken to mean that it is found on trees, but it is 

 to be sought for among the vegetation and debris at their bases. 

 Vitrina (glass shell) has in Colorado a single representative, 

 called by Dall V. alaskana. It is pale greenish, excessively thin 

 and fragile, with an extremely large aperture. When alive, the 

 animal is seen to be very large and exposed, so that there is some 

 resemblance to a slug. One would suppose that such a creature 

 would be very susceptible to cold, but actually it crawls about 

 in cold weather, when most other snails have gone into hiding. 

 There is even a species of Vitrina living in Greenland. The 

 transparent shell permits the pulsations of the heart to be seen. 

 In the case of the English Vitrina it was noticed that the heart 

 beat 51 times a minute when the snail was on a cool table, but 

 when it was placed on the warm hand of the observer, the 

 beats increased to 98. 



