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Zoology of Colorado 



to the large marine limpets so common on the sea shore. Our 

 recorded Colorado species of freshwater limpet is a member of the 

 American genus Ferrissia, but Professor Junius Henderson has 

 lately made the very astonishing discovery of a new species of 

 Ancylus {A. hendersoni of Walker,) in Lake Eldora. This is re- 

 markable, because the genus Ancylus as now understood was 

 supposed to be restricted to the Old World. Evidently we have 

 a survival of the boreal fauna in these cold alpine waters. 



An interesting little snail is the Physa cupreonitens, found in 

 a warm spring, or rather stream running from it at Wellsville in 

 Fremont County. It was discovered by the present writer in 

 1887, and described in 1889, taking the name cupreonitens because 

 of its shining coppery-red shell. In 1924, about 36 years 

 later, Professor Henderson went to the exact spot, and obtained 

 a bottle full of the snails, so that they can now be distributed to 

 collectors and museums. About 17 species of Physa have 

 been reported as living in Colorado, but it is probable that the 

 actual number of valid species is not so great. They should be 

 collected in quantities, and by the study of their anatomy, includ- 

 ing the lingual membrane, it will eventually be possible to define 

 the species with exactness. Our larger Planorbis, with broad 

 whorls, belong to the subgenus Helisoma. The larger one, P. 

 trivolvis of Say, has the shell very variable in size, from 15 to 30 

 mm. in diameter. Although it is difficult to perceive the fact in 

 such a shell, the coil is sinistral; 

 whereas in the other species, P. 

 antrosus of Conrad, it is dextral. 

 This P. antrosus, which is about 1 2 

 to 14 mm. across, was originally 

 named P. bicarinatus by Say, be- 

 cause it has the whorls more or less 

 evidently keeled above and below. 

 Unfortunately Say's name was a homonym; that is, it had been 

 earlier used for another kind of Planorbis, and therefore could not 

 be employed again. Many years ago Ingersoll found a Planorbis 

 living in quantity in St. Mary's Lake, Mineral County, the shells 

 being peculiar for the distortion of the whorls, the coiling being 

 irregular instead of in a single plane. He called this Helisoma 

 plexata, but it has been shown by subsequent writers that it is 



Planorbis 

 trivolvis Say 



Planorbis 

 antrosus 

 Conrad 



