202 J. Starkie Gardner-* On the Gault Aporrhdidce. 



the Geol. and Nat. Hist. Eepert. p. 99, f. 18. A. Robinaldina and A. 

 glabra, from the Lower Greensand, have both been confounded with 

 this species. For the remaining references to A. ParJcinsoni, see A. 

 Mantelli. 



Apoerhais Mantelli, mihi. PL VI. Figs. 8, 9. 

 Synonym : A. ParMnsoni, Mant. 



Description. — Shell elongated, spire composed of convex whorls, 

 ornamented with 12 or more regular, rather oblique, transverse ribs, 

 extending the whole breadth of the whorls. Last whorl destitute of 

 keel. The wing is broad, angular, and quadrate, prolonged poste- 

 riorly into a point, beneath which is a deep sinus, succeeded by a 

 broad, quadrate expansion, which expansion is also frequently pro- 

 longed into a point, parallel to the first, truncated at its outer margin. 

 The mouth is narrow, porcellanous ; the anterior canal moderately 

 long and straight. 



A. Mantelli differs from the Gault form A. ParMnsoni in the fewer 

 number of ribs and their much greater relative prominence. The 

 broad, quadrate expansion is much more truncated, angular, and 

 pointed, both anteriorly and posteriorly. 



Distribution. — It is found in the Grey Chalk of Dover, and, on the 

 authority of Mantell and others, at Hamsey, Leacon Hill, South 

 Downs, etc. ; but the only perfect specimens I have seen have come 

 from a bed of the Grey Chalk known as the cast-bed, between 

 Dover and Folkestone. The condition in which the fossils of this 

 bed are found is peculiar; for although casts, they are not internal 

 moulds of the shells, but the test seems very gradually to have 

 perished without obliterating the external markings, which remain 

 distinct in the form of a thin deposit of sulphate (?) of iron on the 

 mould. Many of the fossils obtained from this deposit are peculiar. 



History. — It will be seen, on referring to the history of A. ParMn- 

 soni, that Mantell first named the Blackdown species Bostellaria Par- 

 Mnsoni, but that he also included the present Grey Chalk species, 

 which bears a strong resemblance to it, under the . same specific 

 name. This shell, however, differs in several specific characters, 

 and requires separating from the Gault form, and does not appear 

 identical with any of the Chalk forms described by Continental 

 authors. I have therefore named it after Mantell, who first described it. 



Among British authors, Dixon, in his Geology of Sussex, p. 358, 

 tab. xxvii. f. 31, 36, describes this shell as A. stenoptera, and Mr. 

 Tate, in ] 865, as A. ParMnsoni. 



Aporehais Mantelli, var. stjb-tuberculata, mihi. PL VI. Fig 10. 



A form exactly resembling A. Mantelli in the shape of the 

 wing and spire, excepting in the last whorl, on which the ribs are 

 divided into two distinct rows of tubercles. The ribs on the re- 

 mainder of the shell are finer, and do not quite reach to the sutures. 

 It is a smaller shell than those from the Grey Chalk of Dover. Com- 

 pare Fig. 10 and Figs. 8, 9. 



Two specimens are in that part of Mr. Cunnington's collection 

 recently purchased by the British Museum. They were found in 

 the Chalk Marl, near Devizes. 



