REV. A. M. NORMAN ON THE CRUSTACEA. 17 



have. also specimens from Plymouth, Roundstone Bay, and Shet- 

 land; and others are in Mr. Gr. S. Brady's collection from Donegal 

 and Preston Pans Thus the species would appear to be distri- 

 buted all round our coasts. 



Cythere avena, Norman. 

 Cythere mytiloides, Norman, Ann. Nat. Hist., January, 

 1862. PI. Ill, figs. 1-3. 

 The specific name, mytiloides, having been previously employed 

 in this genus by Bosquet, it becomes necessary to change the 

 title of the form described by me in the Annals of Natural His- 

 tory. Cythere avena, as it is now proposed to style it, has been 

 taken off both the Durham and Northumberland coasts. The 

 type specimens were from the Firth of Clyde, and I have since 

 obtained it from Arran in Ireland, Boundstone Bay, and Shetland. 



Cythere simplex, n. sp. PI. V, figs. 1-4. 



Elongo-elliptic, cuneiformly produced posteriorly ; greatest 

 height behind the centre ; length to breadth as two and a half to 

 one ; compressed. Ventral margin slightly incurved anteally, 

 and very convex posteally ; dorsal margin straight in the centre, 

 and sloping nearly equally towards each extremity. Anterior 

 extremity well rounded ; posterior considerably produced to a 

 central point to which the dorsal and ventral margins equally and 

 gradually converge. The only lucid spots which I am able to 

 detect are five elongated spots ranged side by side in the form of 

 a fan slightly in advance of the middle of the carapace. Carapace 

 very thin and delicate in structure, transparent, and perfectly 

 smooth, presenting no appearance of punctures or sculpture of 

 any kind. Hinge line perfectly simple ; valves having a broad 

 internal marginal lamella, most developed behind. Length three 

 quarters of a line. 



This is the species which was recorded by me in the report of 

 the dredging of 1862 (Trans. T. N. P. C, Vol. Y, p. 266), 

 under the name of Cythere acuta, Baird. I have since, however, 

 through the kindness of Dr. Baird, had an opportunity of examin- 

 ing the type specimens on which that species was established, 



c 



