118 



body-whorl, which does not become free at the aperture. A distinct columella is present, and 

 this has a peculiar twisted form or is spirally grooved. No umbilicus. Outer lip thin. 



The typical species of Strophostylus are recognised by their thin shell, commonly ex- 

 panded round or oval aperture, surface with simply concentric lines, and twisted columella. 

 The last character, however, is one which is very rarely available, and it may, therefore, be 

 left out of consideration. The surface ornamentation is likewise not constant, for whilst con- 

 sisting in the typical species of transverse striae alone, Hall has described species with longi- 

 tudinal or revolving striae in addition, and the Strophostylus? cancellatus of Meek and Wor 

 then has a regularly cancellated surface. In these cases, the shell comes closely to resemble 

 Cydonema and some species of Holopea, and, if the columella can not be observed, the determi- 

 nation must rest upon the general form of the shell, which has a depressed or slightly elevated 

 spire and a greatly expanded body-whorl and aperture in Strophostylus, whereas in the two 

 last-mentioned genera the shell is more elevated and turbinate and the body-whorl is only 

 moderately large. It is quite possible that these differences may often prove deceptive, but 

 in the numerous fossil Gasteropods in which the mouth can not be observed, it is difficult to 

 point to any other characters by which a generic determination may be effected. 



In the Corniferous Limestone of Ontario occur two or three species of Gasteropods which 

 have the general form of Strophostylus with the cancellated surface of Cydonema or Holopea 

 (in part). The true affinities of these, owing to their imperfect preservation, can not be made 

 out ; but, in accordance with the considerations above brought forward, I shall in the mean- 

 while refer them provisionally to Strophostylus. I have not been able to identify any of these 

 with previously-recorded species, and have, therefore, b en compelled reluctantly to describe 

 them as new. As many of the descriptions of the known species are, however, very incom- 

 plete, it is quite possible that they are not really new. 



145. STROPHOSTYLUS? SCB-GLOBOSUS (Nicholson). 

 (Plate II., Fig. 3). 



Shell globose, thick, with a depressed spire which is hardly elevated above the upper 

 surface of the body -whorl, except close to the aperture. Volutions three, very rapidly increas- 

 ing in size, convex, the body-whorl enormously expanded and somewhat flattened on its upper 

 surface. Height one-third less than the width. Sutures not canaliculated, and hardly 

 marked at all except between the body-whorl and the spire near the aperture. Aperture 

 large, nearly circular, the outer lip meeting the volution above at considerably less than a 

 right angle, and not extending any further forward than the margin of the aperture below. 

 Outer lip apparently not reflected ; inner lip callous ; apparently no umbilicus. Surface 

 with numerous revolving thread-like strias, of which five occupy the space of one line, and 

 which are crossed by elevated thread-like transverse striae, -which are directed obliquely back- 

 wards, and of which about three occupy the space of one line, thus giving rise to a system of 

 oblong cancelli. 



Height of specimen fourteen lines; width, twenty-two lines; height of aperture, thirteen 

 lines ; width of aperture, thirteen lines. 



From S. globosus (Ha\\), the present species is separated by its larger dimensions, its non- 

 canaliculated suture, and its much more distinct cancellation. From Strophostylus ? cancellatus^ 

 of Meek and Worthen, it is separated by the fact that the outer lip does not meet the 

 volution above at a right angle, and is not prolonged further forward than the lower margin of 

 aperture, whilst the shell appears to be much larger and more globose, and the cancellation 

 is more distinct and pronounced. 



Locality q,nd Formation. Corniferous Limestone, Port Colborne. 



146. STROPHOSTYLUS? OVATUS (Nicholson). 

 (Plate II., Fig. 10). 



Shell transversely elongated or ovoid, the height being to the width as three to five. 

 Spire small, moderately elevated ; volutions three, regularly convex ; the sutures apparently 

 linear, and not canaliculated ; the body-whorl ventricose and especially dilated near the 



