THK NAUTILUS. 



position more like that of var. percarinatus (fig. 12). Two addi- 

 tional specimens from the original locality, submitted by Mr. 

 Nylander, agree very exactly with the Michigan form. 



Mr. Nylander writes in regard to the habits of this form : 

 "I think the variety portagensis lives in comparatively deep 

 water, say 25 feet or so as only a few good specimens have been 

 collected and these have always been " dead " shells. The speci- 

 mens from Cross Lake were dredged in 25 feet of water. 



This raises a question as to whether the inflated form of this 

 variety is not correlated with its habitat in deep water as sug- 

 gested by Pilsbry in regard to the Physa and PlanorUs from 

 Lake Patzcuaro, Mexico (Proc. P. A. N. S., 1891, p. 324). 



A parallel case is found in Lymnsea mighelsi W. G. Binn, 

 which in Michigan, at least, lives in deep water a large part of 

 the year (See Naut., XIV, p. 8). In fifteen years' collecting at 

 Pine Lake, Marquette Co., Mich., I have found this species only 

 twice in shallow water and then in considerable numbers, but 

 only for a few days. It seems likely that the peculiar form of 

 Physa lordi Bd. is to be accounted for in the same way as in 

 Michigan; at least, it is found only in the larger inland lakes. 

 Planorbis muUivolvis Case is also apparently a deep-water species 

 (Naut., XXI, p. 61). 



VIII. Var. ROYALENSis n. v., pi. I, fig. 11. 



Shell thin, light greenish horn-color; superior carination promi- 

 nent, rounded, not acute; basal carina very strong, not acute, but 

 forming a heavy, rounded cord around the deep, funicular umbilicus; 

 upper surface concave, but more or less flattened and not as deep as 

 the umbilicus; sides flattened and narrowed towards the base and 

 contracted just above the basal carina; lines of growth strong and 

 distinct, the sides being longitudinally coarsely and irregularly stri- 

 ated; revolving sculpture strong and distinct; aperture triangular, the 

 upper side very nearly straight and almost flat, meeting the lip at 

 nearly a right angle; acutely angled below; lip thin, sharp, not ex- 

 panded. Alt. 10, diam. 15; height of body whorl in front of aperture 

 5 mm. 



Types (No. 29163, Coll. Walker) from Siskowit Lake, Isle Royale, 

 Lake Superior, Michigan. Cotypes in the collection of the Pliila- 

 delphia Academy. 



About twenty specimens of this strongly characterized form were 



