MICHIGAN ACADEMY OF SCIENCE. 93 



Triodopsis. Stenotrema. 



P. albolabris (Say.) P. monodon (Rack.) 



P. exoleta (Binn.) 



P. multilineata (Say) P. hirsuta (Say) 



P. profunda (Say) 



P. mitchelliana (Lea) 



P. pennsylvanica (Green) 



P. clausa (Say) 



P. elevata (Say) 



P. sayii (Binn) 



P. palliata (Say) 

 P. tridentata (Say) 

 P. fraudulenta PUs. 

 P. inflecta (Say) 



On the accompanying maps the distribution of the different species is shown by counties. 

 No attempt has been made to indicate the range of any of the varietal forms except in 

 the case of P. monodon, where the range of the well marked variety, P. monodon fraterna, 

 is remarkably different from that of the typical form. 



For purposes of comparison, the occurence of the different species in the Chicago Area as 

 given by Baker is also indicated. The accessible information of the fauna of northern 

 Indiana and Ohio is too meagre to be of any practical service. 



From our present information only two species can be said to have a range over the 

 entire state. These are P. albolabris and P. ynonodon fraterna. 



The recorded range of these forms is shown on Plate I. 



It is interesting to notice how closely the records of the two species coincide. In the 

 majority of cases, where one of them has been found, the other occurs also and in several 

 other instances where only one has occurred in a particular county the other has been found 

 in a neighboring one. The fact that while P. albolabris is the largest of our species, and 

 therefore less likely to be overlooked by the average collector, P. monodon fraterna is next 

 to smallest in size, is also of importance as tending to show that the other species were 

 not overlooked by the collectors furnishing these records. On the other hand, it is to 

 be borne in mind, that these species, being of general distribution, probably occur in greater 

 abundance than the allied species, whose range is apparently more limited, and which 

 may occur only in localities specially adapted to them, and hence more likely to be missed 

 by sporadic collecting, such, as must be admitted, is the basis of a large proportion of the 

 present records. The most that can be safely said at the present time is, that in the coun- 

 ties where these two species have alone been found, the others did not occur in the partic- 

 ular localities vLsited by the collector. 



Plate I is also a fair exhibition of the extent of our present knowledge of the distribution 

 of the moUusca in the different counties of the state and, unfortunately, of the still greater 

 extent of our ignorance on that subject. It will be observed that while the southeastern 

 portion of the state and the Saginaw-Grand Valley has been fairly well covered, the whole 

 region north of the Saginaw-Grand Valley with the exception of the shore counties, is 

 practically unexplored. There is also great need of more work in the southwestern por- 

 tion of the state. The importance of extending our knowledge over these unknown por- 

 tions of the state will be mentioned later. But it is obvious that, in the present state of 

 affairs, in regard to most of the species, any attempt to generalize would be futile, and any 

 statements in that direction must be considered as tentative only. So far as the two species 

 indicated on Plate I, however, are concerned, it may be fairly said that they will be found 

 in suitable localities in all portions of the state. 



On Plate II is shown the recorded range of four species of Triodopsis i. e. P. exoleta, multi- 

 lineata, profunda and thyroides, which apparently have a general range across the state 

 south of the Saginaw-Grand Valley. The occurrence of some of these species in counties 

 lying north of the Valley, would tend to indicate that some or all of them have a more 

 northern limit than the present records would support. The almost entire absence of 

 records from this region is a matter of great regret and, until this deficiency is supplied, 

 the question must necessarily rest in abeyance. The occurrence of two species as far north 

 as Chippewa County is very striking. But, although these records have been checked by 

 the inspection of specimens, it would be very desirable to have them verified. 



Judging from the records, P. profunda is not as generally or, at lea-st, as abundantly 

 distributed in the southern part of the state as the other specties given on this plate. How 

 far this is true is another question that must be left to the future. 



The five species of Triodopsis shoA\Ti in Plate III are all apparently, of very limited oc- 

 currence in the state, and any further information in regard to them would be very 

 desirable. 



The single record of P. mitchelliana is based on a single specimen from the collection 

 of the late Dr. G. A. Lathrop of Saginaw and now in the collection of the writer, said to 

 have been found at Armada, Macomb County. It was listed by him as P. clausa. 



