300 CEYLON PEARL OYSTER REPORT. 



reduced in thickness higher up. Verrucae occur all round and have the form of 

 truncated coues, about 0'5 millim. in height and about 1 millim. in diameter at the 

 base. The intervals between them vary greatly, from 2 millims. to almost nil. The 

 surface is covered with pebble-like spicules predominantly oval in shape and neatly 

 fitted together like a mosaic of rounded fragments, which show almost no trace of 

 overlapping or imbrication. Smaller oval scales occur outside the verrucae and 

 spindles project very slightly from within. 



The large coenenchyma spicules are mostly warty irregular ovals, but some are 

 almost rectangular and others are like flint axe-heads. 



They give the following measurements in length and breadth in millimetres : 

 0-55 X 0-35; 0'5 X 0'32 ; 0'4 X 0"3. 



Various kinds of spindles occur : () large thick forms, very warty, measuring 

 0'3 millim. by 0'15 millim., 0'45 millim. by 0'175 millim. ; (b) long thin curved or 

 straight forms, with smaller tubercles or almost smooth, measuring 0'5 millim. by 

 0'03 millim., 0'45 millim. by 0'03 millim. ; and (c) minute warty spindles, O'OG millim. 

 by 0'02 millim.; 0'08 millim. by 0'02 millim. 



Besides these forms there are others which approach the club-type, and are 

 probably modifications of the large spindles. 



Locality : Deep water off Galle. 



Acis ceylonensis, n. sp., var. imbricata, n. 



Another specimen, measuring 4 centims. in height, with only hints of branches, 

 showed a general superficial resemblance to Acis ceylonensis, 11. sp., except that the 

 large coanenchyma spicules were much less regular in form and were much imbricated. 

 An examination of the spicules showed the following forms : 



(1.) Large, modified fusiform, elaborately tuberculate, of very various dimensions, 

 e.g., 0'5 millim. by 0'25 millim.; 0'65 millim. by 0'4 millim.; 1 millim. by 0'5 millim. ; 

 without the monticular prominences characteristic of Acis orientalis. 



(2.) Large rounded or almost oblong tuberculate scales, of various dimensions, e.g., 

 0*35 millim. by 0'4 millim. ; 0'5 millim. by 0'45 millim. 



(3.) Tuberculate clubs, with the ends often much swollen, often 0'45 millim. in 

 length by 0'2 millim. in maximum width ; 0'35 millim. in length by 0'2 millim. in 

 maximum width. 



(4.) Tuberculate spindles, about 0'35 millim. to 0'4 millim. in length by O'l millim. 

 in breadth, some 0'25 millim. in length by 0'05 millim. in breadth. 



This specimen obviously differs markedly in the details of its spiculation from that 

 which we have named Acis ceylonensis, but it may be sufficient to erect a variety 

 within the species. Until more data accumulate it seems quite impossible to tell how 

 far marked differences in spiculation can be relied on as specific. 



Locality : Trincomalee. 



