SPECIAL REPORT ON THE MOLLUSCA. 



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 castaneus, Ingersoll. 

 MicropTiysa Bigersolli, Bland. 

 Fupilla alticola, Ingersoll. 

 Selisoma plexata, Ingersoll. 



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

 on the eastern slope of the range, iilthough 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 Melisoma) had a very local distribution. 

 The genera Zonites, Vitrina, Vallonia, Pupa, Succinea, and Pisidium 

 were widespread. Among the Helices, Patula Gooperi only occurred in 

 broad open valleys ; Patula slriatella and Cronlchitei were found together 

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

 latter replaced striatella. The little Micropliysa, occurring abundantly 

 on the cliifs in Baker's Park up to 11,000 feet, and in the Animas and 

 other valleys draining into the Rio San Juan, was also found in the J^orth 

 Park by Mr. Barber, but his examj)les were less robust. All the other 

 species of this genus belong to Florida and the Gulf coast. The Pupce 

 were perhaps the most common forms, increasing as we went south, 

 where specimens of Vertigo californica and Pupilla alticola were numer- 

 ous everywhere on the mountains as high up as timber grows. Pupilla 

 Blandi, heretofore known only as a fossil in Missouri Eiver Drift, was col- 

 lected alive in considerable numbers. 



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 Eocky Mountains on the east and the Sierra Nevada 

 on the west, designated, by Mr. W. G. Binney, The Central Province 

 (Bulletin Mus. Comp, ZooL, III, ix), I have inserted in their proper system- 

 atic place the names of 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. A brief mention of the 

 range extralimital to the scope of this paper is added to most species. 



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 had access to, leaving to others such deductions as the facts may 

 warrant. Enough is presented, however, it seems to me, to show that the 

 Central Province, so-called, is not so deficient as has been supposed, 

 either in the number of species or in representatives of adjoining faunas. 

 The imj)ression that this inter-montanic region is unfavorable to the 

 development of Pulmonates also seems wrong, except in respect to the 

 scarcity of lime, to which cause we may i3robably attribute the fact that 

 the more minute forms are in large majority. A further discussion of 

 the geographical and hypsometric distribution of the Mollusks of the 



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