324 Mr. J. Alder on new species o/Rissoa and Odostomia. 



three rows of spots on the body whorl. Whorls five or six, not 

 much rounded, terminating in a rather fine point, which is tipped 

 with purple : the upper whorls smooth ; the penultimate and half 

 of the last whorls generally marked with numerous very delicate 

 and faint ribs or plicae, about thirty in number, the bases of which 

 are crossed on the body whorl by a few faint spiral striae, giving 

 that part a reticulated appearance. The whole of the markings are 

 very delicate and sometimes entirely wanting. Aperture mar- 

 gined with yellowish brown, rather small, straight at the pillar, 

 and slightly angulated at the base beneath it. Outer lip thick- 

 ened by a rib behind. Inner lip scarcely reflected, with a slight 

 depression behind. Length about one-tenth of an inch ; breadth 

 half its length. 



T Animal white, with two long setaceous tentacula, having the 

 eyes at their external base. Head bilobed. Foot slender, pro- 

 duced in front, white, with a black spot in the centre of the pos- 

 terior part. The sides have two lobe-like appendages, as is usual 

 in Rissoa, which are margined with dark purple or black : two 

 other lines of the same colour on each side run parallel to these ; 

 the upper one on the side of the back, the lower bordering the 

 foot. The rest of the body is white with some blotches of yellow. 



Found on corallines from deep water, Cullercoats, Northum- 

 berland. 



The shell differs from R. interrupta in being smaller, more de- 

 licate and glossy, as well as in being striated ; from R. semistriata 

 in being ribbed ; and from R.punctura in the less rounded whorls, 

 the more delicate markings, and the transparent and glossy ap- 

 pearance. 



One individual only has occurred of the size mentioned. Se- 

 veral smaller specimens were obtained, some of which, having the 

 rib behind the pillar, appear to be full-grown, but are not above 

 half the size, and are shorter and more ovate in the outline. The 

 I other characters are the same. 



Rissoa costulata. Plate VIII. fig. 8 and 9. 



R. costulata, Risso, UEurop. Merid. iv. p. 119. 



Shell pale yellowish brown or purplish, ovate-oblong, produced 

 at the apex and tapering to a fine point, with eight whorls ; the 

 four upper ones small, flat and smooth, the other four costated 

 and rounded, especially the penultimate one, which generally 

 bulges out beyond the rest. Ribs about ten, strong and promi- 

 nent, swelling in the centre of the whorls : they seldom reach 

 above half-way down the last whorl, which is covered with slightly 

 undulating spiral strise, most conspicuous at the base, and con- 

 tinued up the second and third whorls between the ribs : these 

 strise are variable in strength and sometimes nearly obliterated : 

 the ribs also are occasionally wanting on the last whorl. Aper- 

 ture small, entire, nearly circular, a little contracted above. Outer 



