﻿PLATYOSTOMA. 190 



Remarks. — The above description is taken from the first of these shells, which 

 I at first thought to be distinct from the other two. Afterwards, upon re- 

 examining them in company with Mr. Thomas Roberts, F.G.S., we came to the 

 conclusion that they were all of one species, and that they belonged to Acroculia 

 sigmoidalis, Phillips, the type specimen of which is in the Museum of Practical 

 Geology, and is a small and much-crushed shell from Hope's Nose. In this shell 

 the " much-bent striae, reticulated on the outer part of the whorl," described by 

 Phillips, are decidedly coarser than they are in our own examples. 



These Lummaton fossils very closely approach the group of Capulidae, with 

 well-developed spires, oblique mouths, and a single spiral furrow running up a 

 short distance from the front of the outer lip. The grouping of the ornament into 

 sets is peculiar, and is more easily observed on the mould than on the exterior of 

 the shell itself. It is either formed by the threads being occasionally a little 

 stronger, or by slight undulations in the growth of the shell itself. 



Our species seems identical with the shells referred by Giebel 1 and Kayser 2 

 to Acroculia naticoides, F. A. Homer. 3 The undulating longitudinal striation is 

 the same in each ; and the chief difference between them, as far as I can see, is 

 that the English form is a little less oblique. This might easily, however, be 

 accounted for by supposing a little contortion to have occurred in the course of 

 fossilization. I cannot, however, think that the two later authors are correct in 

 identifying their fossil with Homer's species. That shell seems totally different in 

 shape, being much more globular with a much higher body- whorl ; and its striae 

 form a single slightly arched curve instead of being regularly undulating, as in 

 their German and our English shell Kayser refers it to the genus Platyostoma, 

 Hall, and states that Natica gregaria, Barrande, MS., is probably the same 

 species. No signs of the reticulation which is observable upon Phillips's type 

 specimen appear to be visible on any of the German shells. 



Affinities. — In Pileopsis lineata, Golclfuss,* the spire is much larger, and the 

 longitudinal lines much less undulating. 



1 1858, Giebel, 'Sil. Fauna Unterharz.,' p. 26, pi. iii, fig. 7. 



2 1878, Kayser, ' Abhandl. Geo!. Specialk. Preuss.,' Band ii, pt. 4. p. 100, pi. xvi, figs. 4, 4a. 



3 1852, F. A. Romer, ' Beitr.,' pt. 2, p. 101, pi. xv, fig. 16. 



* 1844, Goldfuss, ' Petref . Germ.,' vol. iii, p. 9, pi. clxviii, fig. 2. 



