OV HEBRIDEAN CEUSTACEA^ ECHINODERHATA, POLYZOA, ETC. 193 



posterior side extremely short and sloping downwards, without any of the 

 angularity which characterizes M. bklentata ; in front gently curved ; on the 

 anterior side considerably expanding and rounded ; on the back rising to- 

 wards the anterior end : heals small, calyciform, bhmt and prominent, 

 incurved, bnt not having any indentation below them ; they are placed 

 close to the posterior side, which is the shortest and not one-sixth the size of 

 the anterior side : li'inge-line rectangular, occnpying about one- third of the 

 circumference : cartilacjc as in J/, bklentata : hiugc-plate narrow and strong, 

 thicker in the middle, not excavated so deeply as in the last-named species, 

 and scarcely at all in the right valve : teeth, in the right valve shoi't, trian- 

 gular, slightly inclining inwards, not widely separated ; in the left valve 

 long, erect, laminar, and parallel with the hinge-line ; the anterior teeth 

 are the largest in both valves : inside iridescent and polished, very finely 

 marked (more distinctly on the anterior side) with slight lines which radiate 

 from the beaks : srars irregularly oblong, conspicuous. L. 0-075. B. 0-1. 

 Habitat. Muddy ground in the Minch, off the north-west coast of Eoss- 

 shire, in 50-60 fathoms. I there found only a single dead specimen ; but 

 twenty years ago I dredged another in Skye, which I deferred noticing until 

 quite satisfied of its differing from M. bidentata. [Since this Eeport was 

 presented, Mr. Dawson has found two more specimens in some of the di-edged 

 sand which I had sent him.] Among the shells procured by Professor 

 LiUjeborg in Bohuslan, on the south coast of Sweden, I observed two or three 

 specimens of the present species, one of which he kindly gave me. 



This shell is smaller than M. bidentata ; it may also be distinguished from 

 that species by its narrower shape, being convex instead of compressed, 

 having a glossy surface, and by the posterior side being extremely small, with 

 almost a perpendicular truncation. That side in 31. bidentata is invariably 

 squarish, and more or less angulated. The teeth in the right valve of M. 

 tumidida are much smaller, and less widely separated by the cartilage-pit ; 

 they are triangular instead of leaf -like, and slightly incline inwards instead 

 of being erect. 



M. truncata of Searles Wood, from the Coralline Crag, is a comparatively 

 large, squarish, and flattened shell, and has long cardinal teeth. 



Report of the Committee appointed for the purpose of Exploring the 

 Coasts of the Hebrides by means of the Dredge. — Part II. On the 

 Crustacea, Echinodermata, Polyzoa, Actinozoa, and Hydrozoa. 

 By the Rev. Alfred Merle Norman^ M.A. 



Mr. Jeffreys having, in his Eeport upon the MoUusca, already given to the 

 Association an account of the district investigated by the Committee, aud of 

 the scope of their dredging-operations, it is unnecessary that I should add 

 more on that subject; and I shall therefore proceed at once to lay before 

 you a brief summary of the results of the dredging with respect to the Crus- 

 tacea, Echinodermata, Polyzoa, and Ccelenterata, 



Although the Hebridean seas had been frequently dredged by the natu- 

 ralists who were well acquainted with the Mollusca, they had been scarcely 

 at all examined by any one conversant ■nith the other branches of the marine 

 invertebrate fauna ; aud the result of the recent investigations has thus been 

 most important. This will be at once evident when it is stated that, in addi- 



1866. 



