420 MACTRIM. 



than fringed: tubes clothed with an evanescent epidermis, 

 varying in colour from white to yellowish or reddish ; their 

 sides are scabrous at intervals, and the excreta! tube is rough 

 with a serrated keel, as well as furnished with the usual re- 

 tractile valve ; orifices fringed with a double row of white, 

 yellow, or pale-red cirri : gills and palps light brown : foot 

 narrow and tapering, yellowish- white. 



SHELL so closely allied to M. solida, and particularly to its 

 variety elliptica, that I will content myself with pointing out 

 the leading characteristics in which it differs from that species. 

 This is much smaller than the typical form of M. solida, more 

 convex, distinctly and strongly angulated on both sides, in 

 consequence of which a large lunule-shaped depression is 

 formed in front of the beaks, and another at their back ; it is 

 deeply and regularly striated or grooved in those parts, as well 

 as frequently on other portions of the surface ; the umbones 

 also project considerably more than in either the above form or 

 variety, owing to the contraction and angularity of the sides. 

 L. 0-8. B. 1-1. 



Var. 1. striata. Shell larger and thicker, its margins re- 

 presenting almost an equilateral triangle, extremely gibbous, 

 more deeply and thoroughly striated. M. striata, Brown, 111. 

 Conch. G. B. & I. p. 108, pi. xli. f. 10. 



Var. 2. incequalis. Shell resembling the last in every re- 

 spect but the proportional length of the sides, the posterior 

 being obliquely produced to a wedge-like point. 



Yar. 3. tennis. Shell more ventricose, but expanded, of a 

 much thinner texture, longer in proportion to its breadth, 

 smooth or but very slightly and irregularly striated in front, 

 although having the usual grooves or ridges on the dorsal part 

 of each side. 



HABITAT : With the last species and equally diffused, 

 from low- water mark to 27 fathoms. Var. 1. Exmouth, 

 Irish coasts, west of Scotland, and Lerwick. Var. 2. 

 Lough Strangford (Adair) . Var. 3. A single valve only, 

 dredged in 78 fathoms, 40-50 miles south-east of the 

 Whalsey Skerries in Shetland. This remarkable variety 

 is not unlike M. stultorum in shape and consistency; 

 but it has the peculiar dorsal grooves and striated late- 



