196 



Outer surface with 40 radial, low, broad, round ribs, with 

 linear interspaces, slightly crenulating the margin. Obsolete 

 accremental growth-lines cross the ribs. The general colour 

 is a sordid white, and the surface is mostly eroded. The 

 interior is bordered with a narrow continuous band of a grey 

 colour, articulated with 40 equidistant blackish-brown 

 radially arranged spots, corresponding with the intercostal 

 spaces. The spatula is well marked, bluish-white, with dis- 

 tinct muscle-scars rather wide in front, so as to give it a 

 decided neck, beyond which it projects with a convex end. 



The radula consists of 105 rows of teeth with the for- 

 mula 2 (3.0.3.) 2, or more correctly 2 ( i^. i. o. l. ri ) 2. The 

 marginals are simple, bent nearly at a right angle in the 

 middle, with straight stems and curved cusps. The outer 

 laterals are in line with each other, the inner of the two is 

 only about half as wide as the other, with distinct cusps but 

 with united bases which (though the radula may be picked 

 to pieces) are inseparable. The inner laterals are at a higher 

 level, and are close to each other, but their bases are quite 

 separable. There is no central tooth. It has a triangular 

 branch] a extending from the left over the neck to the right, 

 without any branchial cordon. 



Dimensions.— Length, 31'5 mm. ; breadth, 23 mm. ; 

 height, 14 mm. ; height of the curve at the border, 2*5 mm. 



Locality. — Type from Cape Naturaliste. 



It is found also in abundance on Rabbit Island, King 

 George Sound, and at Ellensbrook and Yallingup, south of 

 Cape Naturaliste. 



It lives on the shell of Patella neglecta, Cray. Nearly 

 every example of which above 25 mm. in length carries one 

 or more (hence its name). 



Variations. — It may grow to the size of 41 mm. long by 

 32 mm. wide and 21*5 high. The ribs may increase to more 

 than 50. 



The outer surface is generally much eroded, so that the 

 apex is absent. In one example, 18 mm. by 13 mm. by 

 5 mm., the top is a brown point without any sign of a spiral, 

 '5 mm. by "25 mm. in size surrounded by a white area 2 mm. 

 by 1 mm., from which project 9 primary rays. These in- 

 crease rapidly by splitting and by intercalation to 23 at the 

 margin. 



The blackish markings inside the border vary with the 

 number of ribs. They may be very distinct, but in the 

 larger shells they fade out and may disappear altogether : 

 sometimes in the smaller shells they may be very faint. The 

 narrow marginal band may be so dark as to quite obscure 



