36 



ture, the number and position of its muscular scars,, and 

 flat (instead of raised) plug. It is also not so susceptible 

 of outward impressions as that species. An A. patelli- 

 formis attached to a scallop, although it sometimes par- 

 takes of its companion's ribs, has also its own natural 

 ribs, which run their independent course from the beak 

 to the margins. The orifice in young specimens is 

 nearly round. The prominent beak somewhat resem- 

 bles the apex of a limpet. The plug lies in a hollow, 

 which is apparently made in the same way as I have 

 suggested with regard to the other species. Owing pro- 

 bably to the green colour of the liver, the rostral area 

 or nucleus of the shell always appears to have a similar 

 tinge. 



It is not without considerable hesitation that I have 

 ventured to unite with this species the A. striata of 

 Loven ; but, after examining his types at Stockholm, 

 and a long and careful comparison of a great many 

 specimens of this beautiful variety, I cannot make out 

 any definite specific character. The only difference 

 consists in the more delicate sculpture of LoveVs shell; 

 and specimens may be observed in which the ribs and 

 striae blend so insensibly into each other, that it is im- 

 possible to say whether they belong to the typical spe- 

 cies or the variety. Judging from Linnets description 

 of A. patelliformiSj this variety appears to correspond 

 with it better than the typical form. I consider it ana- 

 logous to the variety ' ' aculeata " of the last species. 



A. patelliformis has not received so many names as 

 A. ephippium, and I can only find fourteen of them. 

 The Ostreum striatum of Da Costa (but not that of 

 Lister) appears to be this species. It has been placed 

 by some conchologists in the genus Placunanomia of 

 Broderip; but the distinctive character of that genus 



