50 Studies in Geology, No. 3 



than two-thirds the length of the shell, regularly convex, 

 depressed above the shoulder, which is large and strong, 

 and forms a very distinct ridge, extending more than half 

 around the shell. The upper whorls are marked by a series 

 of longitudinal ridges, eight or ten to a whorl, and crossed 

 by strong, equidistant, revolving lines. The two lower 

 whorls are destitute of the ridges, but ornamented by revol- 

 ving lines, which become more or less indistinct on the body 

 whorl in mature specimens. The base of the body whorl is 

 marked by much stronger lines. Variable in size. Aperture 

 oblong-oval ; outer lip thin. Canal long and slightly reflexed. 

 Umbilical chink bordered by a broad keel. Measurements 

 as follows: length 43.2; breadth (at shoulder) 30.6; breadth 

 (below shoulder) 28 mm." — Nelson, 1870. 



The aperture is marked by a heavy inner callus, which is 

 strong posteriorly, and bears the recurved notch characteris- 

 tic of the genus. Grzybow^ski's figure (q.v., loc. cit.) shows 

 this feature better than does the material available for the 

 present study. 



The occurrence of this species, the second of the genus to 

 be known, in the Miocene of Peru, is of unusual interest. 

 The specimens in both the Nelson and Hopkins collections 

 lack the full aperture, and the presence of the heavy, callus 

 posterior lip characteristic of T. distorta Wood, from Pan- 

 ama, the type of the genus, is not clear. Grzybowski (loc. 

 cit.) apparently had a specimen with the full aperture pre- 

 served, and although his figure is not all one might ask, it 

 shows that the species is aperturally configured much as is 

 T. distorta, and is undoubtedly of the genus. Grzybowski, 

 referring his shell to Pyriila Lamarck, apparently thought 

 that the basal portion of the columella had been broken off, 

 and drew dotted lines below to indicate the continuation of 

 the shell, whereas his shell was really perfect basally ; in 

 reference to his figure it is accordingly necessary to disregard 

 the lines added by him. 



The genus, typically of the West Coast, is thus seen to 



