OF CONCHOLOGY. 269 



thej consist of a row of alternately large and small laminiie, of 

 a suboval shape, flattened or slightly concave on one side, and 

 rather prominently convex on the other ; each composed of two 

 walls of very thin vascular membrane united by a somewhat 

 denser layer at the outer border, and filled with fluid (whether 

 water or natural serous fluid being yet undetermined) while they 

 they are still further strengthened by a series of internal fibres 

 which cross each other like the braced timbers of a worked-out 

 mine. The external surface of the branchiae is ciliated, and the 

 whole mechanism presents analogies with the gills of Lamelli- 

 branchs. It is probable that the lamellae of the gill in Acmcea, 

 though differently placed, are of essentially similar construction, 

 while dift'ering in form. The blood is transparent and the cor- 

 puscles are very small. 



According to Dr. Williams, the lining membrane of the bran- 

 chias is continuous, and it is highly improbable that water pene- 

 trates into the system as in some other mollusca. Lankester 

 (An. Nat. Hist. 3d ser. xx, p. 334, 1867) describes two orifices, 

 (capito-pedal), " one on each side of the head, in the angle formed 

 by its junction with the muscular foot, and opening into the 

 blood sinus surrounding the pharyngeal viscera." He also de- 

 scribes a communication which he supposes to exist between the 

 "pericardium and the supra-anal articulated sac," or accessory 

 renal organ. 



My opportunities for examination of the present species hav- 

 ing been confined to alcoholic and very limited material, I do 

 not assume to speak positively in this matter, but can only say 

 that the most careful search, assisted by injections from within, 

 and the most thorough scrutiny of all the external anterior sur- 

 face of the animal with a high power, failed to disclose either of 

 the orifices alluded to. Moreover the search was not confined to 

 this species, but was made in every species, and even specimen, 

 examined, with a like result. In Oollisella patina the heart is 

 situated behind the left side of the head, very far to the left, and 

 entirely away from the renal sac, which last is much smaller than 

 in Patella vulgata ; hence it appears highly improbable that any 

 communication whatever exists between them ; and if this be the 

 casein a species closely allied, it adds to the improbability of the 

 existence of such a communication in the present species. Mr, 

 Lankester's paper is so exceedingly brief that it is not easy to 

 follow his dissections, and it is greatly to be desired that a fuller 

 account, with figures, which he promises, should be published. 

 There is a bare possibility that the contraction of the specimens 

 may have entirely obscured and closed up the openings of the 

 supposed "capito-pedal orifices," or they may not exist in the 



