SPECIAL REPORT ON THE MOLLUSCA. 



By Ernest Ingersoll, Zoologist. 



The collection of mollusks fairly represents the land and fresh-water 

 families, and comprises many additions to the fauna of Colorado, as well 

 as the following six species, believed to be new : 



Limax montanus, Ingersoll. 

 Limax castanetis, Ingersoll. 

 Microphysa higersollii, Bland. 

 Pupilla alticola, Ingersoll. 

 Helisoma plexata, Ingersoll. 



With respect to their distribution : it will be seen that none were found 

 on the eastern slope of the range, although there is no conclusive evi- 

 dence that they do not exist there; that there was a marked increase 

 as we advanced south; that altitude seemed to have little influence 

 upon their range so long as other favorable conditions were present ; 

 and that some species (as of Helisoma) had a very local distribution. 

 The genera Zonites, Yitrina, Vallonia, Fupa, and ^uccinea were wide- 

 spread. Among the Helices, Patula Cooperi only occurred in broad 

 open valleys ; Fatula striatella and GronJchitei were found together over 

 the northern portion of the district traversed, but in the south the latter 

 replaces striatella. The little Microphysa was not found north of the 

 Saguache range, though occurring abundantly on the cliffs in Baker's 

 Park up to 11,000 feet, and also in the Animas and other valleys drain- 

 ing into the Eio San Juan. All the other species of this genus belong- 

 to Florida and the Gulf coast. The Pupoi were perhaps the most com- 

 mon forms, increasing as we went south, where specimens of Vertigo 

 californica and Pupilla alticola were numerous everywhere on the mount- 

 ains as high up as timber grows. 



In order to make this list as far as practicable a statement of our 

 present knowledge of the mollusca of that portion of the United States 

 lying between the Bocky Mountains on the east and the Sierra Nevada 

 on the west, designated by Mr.W. G. Binney the Central Province (Bul- 

 letin Mus. Comp. Zool., Ill, ix), I have inserted in their proper system- 

 atic place such mollusks as I could ascertain to have occurred within 

 that region, distinguishing those species which form my own list by the 

 black head-letter type. 



There seems some reason to doubt whether the limits assigned by Mr. 

 Binney in his Geographical Catalogue, above referred to, circumscribe a 

 true zoological province, considered with reference to the mollusca ; but 

 I have contented myself with carefully tabulating such observations as 

 I have access to, leaving to others such deductions as the facts may 

 warrant. 



Enough is present, however, it seems to me, to show that the Central 

 Province, so-called, is not so deficient as has been supposed, either in. 



