J. Starkie Gardner — Cretaceous Gasteropoda. 161 



Brachystoma angularis, Seeley. Gault. Plate IV. Figs. 11 & 11a. 



Shell elongated, angle 24° ; whorls ten or eleven, elevated, 

 moderately convex ; apex smooth, not acuminated. Eibs twelve, 

 nearly straight, prominent, rounded ; sutural region flat, strongly 

 striated ; strise rounded and undulating, not angulated, crossed by 

 fine lines of growth. The last whorl is angulated and projects 

 beyond the spiral angle ; the ribs are absent on the dorsal side near 

 the aperture, and are replaced by lines of growth ; it also possesses 

 two slight keels, the anterior being but faintly marked. The mouth 

 is sub-pentagonal. The cast is distinctly ribbed and preserves traces 

 of striae, the last whorl being smooth, but with remains of the keels. 



This species is readily distinguished from all others of the Gault 

 by the greater height of the whorls. The wing process is so very 

 reduced that the shell might be taken for a Scalaria ; but the change 

 in character of the last whorl leaves no doubt that it is a true 

 Aporrliais, to which genus indeed Pictet and Campiche had already 

 noticed its resemblance. 



Seeley describes this species in the Ann. and Mag. of Nat. Hist. 

 for April, 1861, p. 6, pi. xi. fig. 9, as Scalaria angidaris, from a 

 specimen belonging to Mr. Carter, of Cambridge. 



Family Eissoid^, Forbes and Hanley. 



No true Bissoa appears hitherto to have been found in British 

 Cretaceous rocks, although a few species have been described on the 

 Continent. 



The UissoidcB were separated from Lamarck's family of LittorinidcB ; 

 since, they have been classified by Schwartz von Mohrenstein, 

 Deshayes, Adams, W. Stimpson, and others, and the family has been 

 divided into as many as seven sub-families and 43 genera, of which 

 only one is now brought under notice. 



The Bissoidce are of especial interest, on account of the gradual 

 transitions found amongst them from aquatic to terrestrial forms. 

 The marine species, however, usually possess a strong, solid shell, 

 and are ornamented with striae or ribs ; the brackish- water forms 

 have a thinner shell ; whilst the shell of the fresh- water and 

 amphibious species is generally thin and smooth. 



ElSSOINA, 



was proposed as a sub-genus, by d'Orbigny, of the raollusca found 

 during his voyage in South America, and later erected into a genus 

 in consideration of the operculum, the muscular impression of which 

 has an elongated process. It is adopted by most classifiers. Schwartz 

 von Mohrenstein ^ has published a monograph on Bissoina, in which 

 is enumerated 91 species, 29 being fossil. Deshayes accepts the 

 genus with hesitation, but gives a minute description of its characters. 

 The Bissoina are small marine mollusca, which live on alg93 in 

 shallow water and in warm latitudes. They are particularly dis- 

 tinguished by the form of their aperture, which is oval, crescentic, 

 narrowed posteriorly, the lips uniting on the penultimate whorl ; it is 

 ^ Denkschriften d. k. Akad. d. Wissensch.-Mathem., 1860, vol 19. 



EECADE II. — VOL. III. — NO. IV. 11 



