340 COXTEIBUTIONS TO CANADIAN PALAEONTOLOGY. 



edly agree better with the descriptions and figures of the shoulderless M. 

 subrostafa than with those of the strongly shouldered 21. arcnlata. 



(S.) jNIaCROCHILINA PULCIIELLA. (N. SjJ.). 



Plate 44, tigs. C and (ia. 



Shell small, the most perfect specimen collected being less than one- 

 third the size of adult specimens of j\L urcuhitn. from Dawson Bay, imper- 

 forate, but pointed above and one-third higher or longer than broad ; 

 spire almost conical, acutely pointed and a little shorter than the outer 

 volution, as measured in the median line of the dorsal surface. Volutions 

 five in- six, those of the spire obliquely com])ressed, the outer one moder- 

 ately convex, slightly inflated, but very faintly constricted above, about 

 as brcjad or a little broader than high and narrowing abruptly into the 

 evenly rounded base : suture impressed, linear and minutely crenulated 

 by the ti'ansverse costulie : apertui'e subovate, higher than wide and occu- 

 pying more than one-half of the entire height, pointed above and rounded 

 below ■ outer lip thin and simple. 



Surface mai'ked with closely and regularly arranged, Hexuous raised 

 lines, or nearly equidistant, extremely thin and acute, minute costuhe, 

 which cross the volutions transversely but somewhat obliquely. 



Dimensions of the specimen figured : height or length, eighteen milli- 

 metres and a half ; maximum breadth, twelve mm. 



South-west shore of Dawson Bay, about two miles west of Salt Point, 

 J. B. Tyrrell, LSSO : one nearly perfect specinien with the test preserved. 

 Three casts of the interioi- of shells which are probably referable to this 

 species, but which do not show ;i trace of the characteristic surface 

 ornamentation, had previously been collected by Mr. Tyrrell and the 

 writer, in 1888, at Pentamerus Point, Lake Manitoba. The largest of 

 these casts is nearly an inch in length. 



This delicately sculptured shell appears to differ from J/, (tfcuhita 

 chiefly in its diminutive size. It has somewhat the same general contour 

 as the Polyplicmo'p.ntt Lmi Ixvil/a/ of Hall and Whitfield,* from the Upper 

 Helderberg limestone at the Falls of the Ohio, but that species is 

 rej)resented as narrow and somewhat pointed at the base, and its surface 

 is stated to be smooth. 



The following description should have followed that of Pleurotomaria 

 iiifrtinridosa, on page 313. 



•Twenty-third Reg. Rep. N.Y. «t. Call. Nat. Hist., 1869, pi. xii, figs. 1 and 2 ; and 

 twenty-fourth do., 1870, p. 193. 



