206 INVERTEBRATA OF MASSACHUSETTS. 



this family, would seem to entitle it to be arranged as a sub-genus. 

 It differs from the preceding in having the umbilicus on the left in- 

 stead of the right side, being its natural place. Mr, Haldeman pro- 

 poses to make this species the type of a sub-genus, which he calls 

 Planorhula. 



Planorbis hirsu'tus. 



Shell light yelloivish-brown, concave on both sides., most so on 

 the left ; lohorls three ; surface beset ivith revolving lines of rigid 

 hairs ; aperture large, very oblique. 



Figure 135. 



State Coll., No. 82. Soc. Cab., No. 1278. 



Planorbis hirsutus, Gould ; Silliman's Journ., xxxviii. 196. 



Shell small, somewhat transparent, of a brownish yellow-color ; 

 both sides concave, the left rather more than the right, but the 

 concavity is there more limited by the presence of a sub-angular 

 ridge on the outer whorl ; whorls three, the outer one rapidly in- 

 creasing ; surface exhibiting traces of revolving lines when de- 

 nuded, but usually covered with a dark pigment or epidermis, 

 bristling with rigid hairs, which are arranged in close revolving 

 lines ; lines of growth very faint ; aperture sub-oval, oblique, its 

 diameter from side to side shorter than in the opposite direction ; 

 its plane very oblique. Long diameter \ inch, short diameter yj 

 inch. 



Animal has the head slate-colored above, with a darker line along 

 each tentaculum, not originating from the eyes ; foot chestnut- 

 colored. 



This shell was first found by Professor C. B. Adams, in Mans- 

 field, from whom I received it. I have since found it in several 

 localities in Dorchester, Dedham, and Cambridge, adhering to 

 sticks in stagnant water ; and it may doubtless be found in all 

 similar localities. 



This Planorbis, though in many respects it resembles in shape 

 P. defectus, is readily distinguished from all other American species 

 by the revolving hairy lines. It is the analogue of the European 

 P. albus, from which it is difficult to designate any very characteristic 

 difference. It is, however, a thinner shell, the last whorl increasing 



