CHTHAMALUS 1NTE11TEXTUS. 



467 



7. Chthamalus intertextus. PL 19, fig. 1 a, 1 b. 



Shell, when well preserved, violet-purple : sutures, when 

 not obliterated, formed by oblique interfolding lamina : basis 

 membranous, but surrounded by a ledge formed by the in- 

 flected basal edges of the parietes ; scutum and tergum com- 

 pletely calcified together. 



Hab. — Philippine Archipelago ; Mus. Cuming. 



General Appearance and Structure. — Shell depressed, with a large 

 diamond-shaped orifice. Colour beautiful violet-purple, but externally 

 much obscured by disintegration, causing the shell to be ashy grey. 

 Walls smooth or slightly folded. Sutures generally quite, or almost quite 

 obliterated ; but when well preserved, they differ remarkably in appear- 

 ance from those in the foregoing species ; for the radii externally here 

 consist of oblique plates or laminae arising on both sides of the sutures, 

 standing nearly parallel to the parietes, and interfolding with each other. 

 These laminae are rather plainly marked by lines of growth. Essentially 

 the radii do not differ much from those in C. dentatus and Hembeli ; 

 we have but to produce obliquely upwards the transverse and inter- 

 locking ribs on their radii, and so convert them into laminae. During 

 the diametric growth of the shell, the sutural edges of the alae are 

 added to, in the usual manner, by upturned lines of growth ; and, in 

 addition, the recipient furrows of the alee are similarly added to, so 

 that the lines of growth are upturned, and alae appear to have been 

 developed on both sides of the sutures in the same way as the radii 

 appear to have been developed on both sides in many Chthamalinse, 

 though rarely in the Balaninse. The inside of the shell is beautifully 

 coloured rich violet j it is punctured with small holes as so often is the 

 case with C. stellatus. In every specimen (all full-grown) which I 

 opened, the inner basal edges of the parietes were inflected rectangu- 

 larly inwards, forming a smooth-edged ledge all round the basal mem- 

 brane, which, in proportion to the width of this ledge, was by so much 

 reduced in diameter. The largest specimen which I have seen was *35 

 of an inch in basal diameter. 



Opercular valves. — The scuta and terga, in all the specimens which 

 I have seen, were firmly calcified together; in some, a trace of a suture 

 could be seen externally, but hardly a trace internally. In one speci- 

 men, there were vestiges of some impressed lines on the scutum, in 

 exactly the same position in which such occur in C. Hembeli. The 

 scutum is rather narrow. The basal margin of the tergum is either 

 straight, or depends a little on the scutal side, thus producing a small 

 spur : the crests for the depressor muscles are strongly marked, and 

 depend beneath the basal margin. 



