CREUSIA SPINULOSA. 379 



Var. (5), PI. 14, fig. 6 m. — Hab. Unknown. — We have seen in 

 vars. 2 and 3 that the scutum varies considerably in shape : here it is 

 unusually narrow, with the adductor ridge almost touching the articular 

 ridge. There is no little tooth near the rostral angle, and the basi-scutal 

 corner is not hollowed out. The tergum also varies ; in some indi- 

 viduals it is truncated and like that figured of var. 1, but rather more 

 rounded ; in other specimens (from the same branch of coral) the basal 

 margin so blends into the spur that the latter can hardly be discrimi- 

 nated (fig. 6 m) ; in other respects the outline resembles pretty closely 

 that of one of the sub-vars. (fig. 6/) of var. 2. The shell is not porose ; 

 it is thick, with strong internal ribs, and resembles that oivar. 1; but 

 it is of a pale purplish colour. 



Var. (6), an. spec. ? fig. 6 n — 6 q. — Hab. Philippine Archipelago. — 

 This is a very remarkable variety ; we have, imbedded in the same 

 coral, and with shells absolutely identical, specimens with the scutum 

 having three distinct but graduated forms. Firstly, a scutum trans- 

 versely elongated, in all external respects like some of the varieties 

 mentioned under vars. 2 and 3, with no rostral tooth, and not hollowed 

 out at the basi-tergal corner, but with the adductor ridge more promi- 

 nent. Secondly, a scutum of the same general shape, but with the 

 adductor ridge so much developed (fig. 6 n) as to descend slightly 

 beneath the basal margin, and to be seen when the valve is viewed 

 externally ; there is a very slight tooth near the rostral angle (as in some 

 former sub-varieties), and which can be here rather more clearly seen 

 than hitherto, to be formed by the adductor ridge (closely united to 

 the external surface of the valve) extending thus far, and being here 

 produced a little downwards. Thirdly (6p), we have the adductor 

 ridge immensely developed, descending far below the basal margin of 

 the ordinary valve ; and the basal margin at the basi-tergal corner is 

 angularly and deeply hollowed out. The appearance of the valve is 

 widely different from that in the first sub-variety, yet it is impossible to 

 separate the first and second sub-varieties, and it is almost equally certain 

 that the third sub-variety is only an exaggeration of the second. The 

 lower edge of the adductor ridge, in the third sub-variety, varies a little 

 in outline ; it is deeply sinuous, and is produced at the rostral angle 

 into a point, of which we have heretofore seen only a feeble represen- 

 tation. It would appear as if the great development of the adductor 

 plate had caused the exterior ordinary surface of the valve to shrink 

 or be less developed. There is a striking resemblance in the structure 

 here described with that in Pyrgoma cancellatum and conjugatum. The 

 terga belonging to the above scuta, also, vary; the spur being sometimes 

 square (6 o), and sometimes bluntly pointed : when the spur runs in 

 the same exact line (6 q) with the scutal margin of the valve, a peculiar 

 aspect is given to it, but this is by no means always the case. Both 

 opercular valves are often partially coloured pinkish- purple. The shell 

 is not porose ; it is thin, with remarkably prominent internal plates ; 

 it is apparently always of small size, which I attribute to this variety 

 inhabiting a hard thin plate-like coral. The sheath is bright pinkish- 

 purple, of which we have had instances in some of the other varieties ; 

 and the shell itself is sometimes pinkish. Taking the scutum of the 



