76 PECTINID.E. 



whatever they lie upon ! Shells sometimes attain an 

 enormous size. Dr. Landsborough says he measured 

 one which was 8 inches long. I have another specimen 

 that is barely -g^th of an inch in length. The young are 

 attached by a byssus. They are quite smooth ; and in 

 the place of ribs a few fine white lines radiate from the 

 beaks, as is not unfrequently seen in P. similis. This 

 might be considered by the advocates of a theory, which 

 was once put forward in the ' Vestiges of Creation/ a 

 case of arrested development as regards P. similis ; but 

 they ought to be aware of the fact that both these species 

 of every age inhabit the same spots and yet retain their 

 own distinctive characters. One species never grows or 

 merges into the other. The young of P. maximus may 

 be known from P. similis of the same size by the upper 

 valve in the former being flat, and in the other convex, 

 as well as by the inequality of the ears in the first-named 

 species. It bears a considerable resemblance to a young 

 Avicula, and shows the affinity which exists between 

 that genus and the Pectinida. The adult seem not to 

 have the power of spinning a byssus, nor to have any 

 occasion for it. Their solid shells can withstand a good 

 deal of buffeting by the tide ; if they were slighter, they 

 would require the cable of a Pinna to hold them on their 

 anchorage-ground. The substance of the shells is very 

 durable. I have had some of the deep valves in frequent 

 use during the last eighteen years for scalloping oysters ; 

 and although they must have been baked in an oven at 

 least five hundred times, they are as perfect and ser- 

 viceable as ever. The prettiest specimens come from 

 Dublin, Cork, and the Channel Isles. 



This species belongs to the genus Vola of Klein. The 

 young is the P. Icevis of Pennant and the older British 

 conchologists. 



