78 



the outer volution appears to be nearly smooth and marked only with a 

 narrow and apparently flat spiral band a little above or on the apical side 

 of the mid-height. Under a lens it seems to be marked with numerous 

 and extremely minute transverse lines of growth, which are crossed by 

 equally minute spiral raised lines, but the specimen is not sufficiently well 

 preserved to show the minute details of the sculpture at all satisfactorily. 



Dimensions of the most perfect specimen, the original of fig. 9 : entire 

 height, as measured in the median line of the dorsal surface, fourteen 

 mm. ; greatest breadth, eleven mm. and a half ; height of spire, five mm. 

 and a half. 



Durham, J. Towsend, 1878-82 : one natural mould of the exterior of 

 the shell (with part of the test of the spire preserved, though its outer 

 surface is buried in the matrix) and four small casts of the interior of the 

 shell. 



This little shell appears to belong to that section of the genus Pleuro- 

 tomaria which Lindstrom, in the memoir previously referred to, designates 

 as the Naticoideoi. According to Lindstrom, only one species of that 

 section was previously known, viz., the P. exquisita of that author himself, 

 from the Silurian rocks of Gotland. The minute surface markings of F. 

 Townsendii, so far as they can be ascertained at present, seem to resemble 

 those of P. exquisita, but in that species the slit band is placed below or 

 on the umbilical side of the mid-height, the spire is shorter and much more 

 obtuse and the base distinctly umbilicated. 



MURCHISONIA. 



I 

 It will be convenient to group the species of this genus that are known 

 to occur in the Guelph formation of Ontario, as far as practicable in their 

 natural order, commencing with the short-spired Pleurotomaria-like forms, 

 and ending with the slender species with very numerous volutions. M. 

 Hercyna, Billings, is now regarded as a Pleiirotomaria ; M. Boydii, Hall, 

 appears to the writer to be a Loxonema ; and Fisher's genus Loxoplocus 

 will be retained for M. soluta (Whiteaves) of which M. tropidophora 

 (Whiteaves) is now known to be A synonym. Specimens of M. hivittata 

 collected at Belwood by Mr. Townsendin 1892, which happen to be broken 

 in such a way as to afford good longitudinal and transverse sections of the 

 empty shell, show that the earlier volutions of the spire are divided into 

 chambers by numerous transverse partitions, also that the columella, 

 which has long been known to be encircled with two spiral folds, is 

 tubular and hollow throughout. 



A. Short spired species, approachingto PZewrotomaHa. Volutions 

 four to seven. 



