THE NAUTILUS. 7 



species, which is really widely distributed, common and very vari- 

 able, even if restricted after eliminating the three following species 

 and some others which are clearly distinct. 



The mussels of the typical and near-typical forms average larger 

 and more inflated. It appears that there are several geographical 

 subspecies ; the following is one of them : 



P, abditum suhrotundum St. {P. subrotundum, The Nautilus XX, 

 p. 19, 1906) The mussel is less inflated than in abditum, averaging 

 smaller, the beaks are broader and less elevated ; rather uniform. 

 Appears to be a northern form ; New England to Ontario, Michigan 

 and northern Ohio. 



P. minits (Ad.), Cyclas minor Ad., Proc. Boston Soc. N. H. I, 

 p. 48, 1841 ; ranged under the syn. of P. abditum by Prime, Mon. 

 Corb., p. 68. Is distinct so far as can be judged from the authentic 

 specimens (3 valves, from Waybridge, Vt.) in the T. Prime collec- 

 tion, but appears to be rather rare. Specimens fairly well agreeing 

 with them have been seen from : Duxbury, Mass. (W. F. Clapp, 

 No. 6969) ; Denisville, Me. (Dr. Jas. Lewis' collection, now Mr. 

 Bryant Walkers' No. 2582) ; Klinger's Lake, St. Joseph Co. Mich. 

 (B. Walker, 6846) ; Ann Arbor, Mich. (H. E. Sargent, No. 3099, 

 none full-grown) ; Cowley Farm, Nepean, Ont. (Justice F. R. 

 Latchford, No. 6929), and apparently Greenport, L. I, N. Y. (J. B. 

 Henderson from Sanderson Smith, No. 675). 



P. regulare Pme., Boston Journ. VI, p. 363, pi. XII, figs. 11, 12, 

 1852. Also arranged under the synonymy of P. abditum, in Mon. 

 Corb., 1. c; certainly not a form of abditum, to judge from the single 

 specimen from " Ohio " in the Prime collection, ranging nearer P. 

 noveboracense Pme., but appears to be distinct. Specimens identical 

 were collected near Douglas Lake, Cheboygan County, Michigan, 

 1911, by Mr. H. B. Baker, Nos. 7084 and 7085, and probably the 

 same near Geauga Lake, southeast of Cleveland, Ohio, by Mr. John 

 A. Allen, 1910, No. 6542. Others were seen before but not recog- 

 nized. 



partite] : generally not so, and the figure shows rather the contrary and, by 

 the way, has the beaks too high and otherwise faulty; "generally light straw 

 color " is exceptional : generally light to dark corneous, often yellowish 

 "cardinal teeth separate" is meaningless; "long. 0.15, lat. [= alt.] 0.14: 

 diam. 0.09 inches" does not agree with " shell elongated," and with the figure 

 " The surface is at times also quite rough and the striae coarse" — conf. with ; 

 " the exterior surface is much smoother " (than in P. noveboraeente). 



