336 PLIOCENE MOLLUSCA. 



Purpura lapillus showing that the Crag varieties incrassata (tig. 1), imbricata 

 (fig. 3), and cannula (fig. 4) differed only in size and in the imbrication of one 

 of them. The fossil now figured from the York Museum presents another 

 connecting link, being an imbricated example of the variety incrassata ; it supports 

 the view taken on p. 119, that imbrication is not a varietal character. 



Purpura tetragon a (J. Sowerby). 



1914. Purpura fetragona, F. \V. Harmer, Plioe. Moll. Clt. Brit., pt. i, p. 116, pi. xi, fig. 6. 



Var. intermedia, S. V. Wood. Plate XXXIV, fig. 28. 



1848 Purpura tetragona, var. intermedia, S. V. Wood, Mon. Crag Moll., pt. i, pi. iv, fig. 7c. 

 1885. Purpura tetragona, Lorie, Arch. Mus. Teyler [2], vol. ii, p. 201, pi. vii, fig. 24. 



Remarks. — The fossil here represented, from the Ipswich Museum, is a well- 

 marked variety of P. tetragona, agreeing more or less nearly with the var. 

 intermedia of Wood. 



Dr. Lorie gives a figure of this variety from the Scaldisienof Holland, obtained 

 at a depth of 52 metres from one of the Dutch borings at Gloes. 



Genus PISANIA, Bivona, 1832. 

 Pisania exigua (Dujardin). Plate XXXV, figs. 22, 23; Plate XLIV, fig. 19. 



1837. Murex exiguus, Dujardin, Mem. Soc. Gt'ol. France, vol. ii, p. 29(1, pi. xix, fig. 2. 



1872. Murex insculptus {?), A. and R. Bell, Proc. Gteol. Assoc, vol. ii, p. 209. 



1874. Murex insculptus, S. V. Wood, Mon. Crag Moll., 1st Suppl., pt. ii, p. 176, add. pi., fig. 9. 



1884. Murex- (Muricopbis) exiguus, Dollfns et Dautzenberg, Feuilles des jeunes Nat., vol. xvi, p. 104. 



1890, Murex insculptus, C. Reid, Plioc. Dep. Brit., p. 247. 



Specific Characters. — Shell small, solid, sub-fusiform ; whorls 5, convex, the 

 last two-thirds the total length; ornamented by strong, rounded, flexuous costa?, 

 8 — 12 on the body-whorl, crossed by rather coarse spiral ridges, with slight 

 tuberculatum at the points of contact, and finer ones in the interspaces ; spire 

 elongate, regularly tapering towards a blunt point; suture distinct, but not deep; 

 mouth irregularly oval, angulate above, contracted at the commencement of the 

 canal, which is short and open ; outer lip thickened by the labial rib, denticulated 

 within ; umbilicus small ; columella with a small tubercle. 



Dimensions.. — L. 10 — 12 mm. B. 5 — 6 mm. 



Distribution. —Not known lrviner. 



