MARINE MOLLUSCA OF MADEIRA. 267 



furrow, across which the tails of the raid-area ridges spread 

 somewhat rudely in coucentric upward-facing curves ; the back- 

 edge of this is a very regular curve from the apex to the point, 

 and which drops rather abruptly into a little shallow furrow, 

 beyond which the thin flat concentrically-undulated posterior ear 

 projects (somewhat as in T. megotara, Hani.), placed rather low 

 but still quite on the shoulder of the shell ; a very shallow obtuse 

 angle lies between this ear and the back margin of the posterior 

 area. Iu the young shell this ear is generally somewhat ob- 

 solete ; the ear-edge is not reverted. Dorsal line not much 

 irregular. Beaks are like smallish round knobs from which, 

 somewhat posteriorly, a minute cup-shaped process projects per- 

 pendicularly, while the apophysis springs from the same knob but 

 a little farther back : it is like that of T. megotara, Haul.; it is a 

 curved, very slightly twisted, shortish narrow ribbon projecting 

 rather directly towards the lower point of the valve ; its front 

 edge is slightly roughened but not thinned out ; the inside is 

 glossy ; above the beak it is shortly reverted along the hinge- 

 line, which is only slightly hollowed out and furrowed. In the 

 belly of the shell two very marked ribs run divergingly from 

 behind the beak to the margin : one, narrow but prominent and 

 well defined, corresponds exactly to the curved sharp impressed 

 line on the outside formed at the junction between the fine 

 horizontal threads of the front area and the stronger perpen- 

 dicular ones of the middle area ; the other has more, though im- 

 perfectly, the character of a projecting shelf to strengthen the 

 attachment of the ear. At the narrowed aud somewhat inturned 

 point of the shell is the usual rouuded tooth or knob. — H. - 15. 

 B. 0-12. 



This species (whose name I have borrowed from my eminent 

 friend of the Washington Smithsonian Institution) is from the 

 south-eastern coast of Madeira, but the precise locality I failed 

 to note. It varies very greatly in the number of the threads on 

 the entire area of its outer surface. On specimens of much the 

 same size I counted of these from 12 to 37. At first sight it seems 

 very like T. Stutchburii, de Blainv. ; but on closer examination 

 the differences stand strongly out, and the two species maybe dis- 

 tinguished at once by the sharp line of demarcation (like that of 

 Xylopliaga dorsalis, Turt.) between the threads of the front area 

 and those which are their prolongation at right angles down the 

 middle area, and the distinction is even more visible in the fine 



20* 



