30(5 MR. G. S. BRADY'S MONOGRAPH OF 



oval • "reatest breadth behind the middle, equal to less than half the length ; the hinge- 

 margins thickened and depressed centrally, so as to form a longitudinal sulcus, but 

 uniting at the extremities, thus forming a broad keel. End view oval, keeled below, 

 sulcata above. The central portion of the valves is covered with a calcareous crust, and 

 1) irs numerous small puncta and a few scattered hairs. Colour yellowish or drab in 

 lecimenfl from beyond low-water mark, brick-red in the littoral variety. The hinge- 

 joint consists (fig. 56), in the left valve, of a long central knurled bar, at each end of 

 which is a fossa for the reception of a corresponding knurled protuberance of the right 

 valve. The right valve differs from the left in being taller and more angularly truncate 



at the extremities. The shell of the male is much more elongate and angular, more 

 deeply sinuated below, and often more rugose on the surface. Colour of the limbs deep 

 brownish yellow. Last joint of the upper antennae very short : terminal spine very 

 slender, almost setose. Feet short and robust; terminal claws strong and curved, 

 that of the last foot indistinctly setose or pectinate on the inner margin. Abdominal 

 lobes short and thick, surrounded with short setae. Copulative organs of the male 



luge, the basal portion quadrangular, the apical portion produced into two tapering 

 prolongations. 



When living in the Laminarian zone, and in deeper water, this species presents some- 

 what different characters : the shell is considerably larger, the dorsal margin generally 

 mow flattened, the surface marked with distant deep punctations, between which are 

 Mattered numerous smaller puncta; the marginal portions tend also to become elevated 

 into irregularly radiating ribs. This latter character is more conspicuous in the male 

 (tig. 47), which is also more distinctly punctate and more angular in outline, the ventral 

 margin especially forming a remarkable angular projection posteriorly. This form is, 

 indeed, so distinct that until recently I supposed it to belong to a distinct species, 

 C. setosa, Baird ; but having now had the opportunity of examining a large series of 

 dredged specimens, as well as a still greater number of carapaces from the glacial clays 

 of Scotland, I cannot avoid the conclusion that it represents merely a deep-water form 

 of the present species, which had previously been known to me only from littoral spe- 



cimens. 



Length (littoral var.) ^ in., height ^ in. ; (deep water var. ) length - 3 \- in., height 



Hob. Abundant in tide-pools on the coasts of Northumberland and Durham, ami in ovster-ooz 



from 



Stranraer (G. S. B.) ; 



<( 



(Dr 



North 



y> 



dredged at Oban and Cumbrae, Macduff and Peterhead (Mr. D. Robertson) ; the 



Jeffreys); Guernsey 



of Laminaria at 



Tobermory (Rev. A. M. Norman) ; Lon- Hope, Orkney (Mr. C. W.Peach). 



This species is found by Sars abundantly on the Norwegian coast, by Zenker in the 

 attegat, and is common also on the northern shores of Britain and in the Arctic 

 ■ n ; I have seen but few specimens from the southern and western coasts of En-land 



Ireland 



It occurs abundantly in a fossil state in the glacial clays of Scotland 



