244 ARCADE. 



but little convex, siibparallel to the dorsal edge, which is 

 straight or slightly subincurved, and horizontal, or barely 

 rising ; anterior side (in this example) more than twice the 

 length of the other ; its extremity a little narrowed, well 

 rounded below, obscurely angulated above. Hinder ter- 

 mination chiefly projecting below the middle ; the oblique 

 convex posterior edge forming an obscure obtuse angle with 

 the dorsal margin ; the lower corner somewhat rounded 

 off. Umbones but little prominent and not far apart. 

 Ligamental area long and narrow. Inside white ; margin 

 indented a little by the external costellse : hinge-margin 

 rather narrow, teeth numerous (about thirty-two). 



The animal is of a pale yellow colour. 



A single small siDecimen of this common Mediterranean 

 shell, which measured fourteen lines in length, and not 

 quite seven in breadth, is said to have been found alive, 

 attached to an oyster at Killinchy in Lough Strangford, 

 County of Down, Ireland, by Dr. Macgee, of Belfast. 

 From this example (still preserved in the cabinet of Mr. 

 Jeffreys), which is precisely identical with those of the 

 Adriatic and Mediterranean, we have drawn up the above 

 description. We have not ventured at present to include 

 this shell positively among our indigenous productions, as 

 no second examj^le of a species usually abundant when 

 present at all, has confirmed by its discovery the indigen- 

 ousness of the recorded one ; nor can we help surmising that 

 there must have been some mistake made about it, for 

 neither the habitat nor locality agree with the ordinary 

 position and range of the species. 



PECTUNCULUS. Lamarck. 



Shell equivalve, equilateral or nearly so, orbicular, closed, 



smooth or striated or with radiating furrows, invested with 



a fimbriated epidermis ; margins plain or crenate ; beaks 



separated by a grooved lanceolate ligamental area ; liga- 



