On the so-called Eyes o/Tridacna. 435 



the body is considerably less than the length of the head, 

 which is one fourth of the total (without caudal). Snout of 

 moderate length, pointed, as long as the postorbital portion of 

 the head ; eye of moderate size. A skinny adipose lobe 

 occupies the place of the enlarged axillary scales of the pec- 

 toral and ventral fins. Back crossed by fourteen narrow 

 brownish bands ; a small deep black spot at the end of the 

 lateral line ; each caudal lobe with four oblique blackish 

 bands ; each dorsal ray with one or two blackish specks. 

 One specimen, 4| inches long. 



LXI. — On the so-called Eyes of Tridacna and the Occur- 

 rence of PseudocTiloropliyll- corpuscles in the Vascular System 

 of the Lamellihranchiata. By J. Beock *. 



Since the investigations of L. Vaillant Tridacna has usually 

 been reckoned among the eye-bearing bivalve MoUusca. As 

 the clam-shells, or at least their smaller species, are among 

 the commonest inhabitants of the Indian coral-reefs, I had 

 sufficient inducement, during my residence in the Indian 

 Archipelago in the year 1886, to undertake a careful investi- 

 gation of these supposed eyes. But owing to the abundance 

 of the tasks wliicli presented themselves on the spot I suc- 

 ceeded finally only in bringing with me to Europe some 

 well-preserved material which has furnished the sole foun- 

 dation of the following description. 



As is well known, the margins of the mantle of the living 

 species of Tridacna are splendidly coloured. The observa- 

 tion of the living animals in their natural position is one of 

 the most charming spectacles which the coral-reefs, rich as 

 they are in beautiful forms and brilliant colours, can present, 

 and the enthusiastic descriptions of travellers (Quoy and 

 Gaimard t, Cuming |, Vaillant §) are in this particular not in 

 the least exaggerated, as I can affirm from my own expe- 

 rience. 



The so-called eyes have no small share in producing this 



* Translated by W. S. Dallas, F.L.S., from the ' Zeitschrift fiir wissen- 

 schaftliclie Zoologie,' Band xlvi. pp. 270-287. The original memoir is 

 illustrated with a plate (pi. xxii.). 



t ' Voyage de I'Astrolabe/ Zoologie, par Quoy et Gaimard, tome iii. 

 (1835), p. 488. 



\ Reeve, ' Conchologia Icouica,' part xiv.. Monograph of Tridacna. 



§ Ann. des Sc. Nat. ser. 3, tome iv. p. 73 (^1865). 



