2ÓO 



Surface of the shell granulated (PI. XXVII, fig. i), with indistinct furrows which extend 

 irregularly over the lower, wider and cylindrical part of the shell, and which radiate from the 

 orifice in the upper, slightly narrower part. In consequence, the orifice is surrounded by a circle 

 of small areas, which are separated from each other by the furrows and which are of a 

 lighter colour, the remaining part of the shell being of a darker, greenish-brown colour. The 

 orifice is elongately-oval, not quite three times as long as broad, small ; its carinal extremity 

 rounded, the rostral one being pointed. 



Shell thick, having srnall and not very distinct pores at irregular distances in the outer 

 layers and having the internal surface strengthened by vertical septa. Sheath not large, 

 extending only to the point where the conical and vertical parts of the compartments meet. 

 Basal part of shell only very superficially embedded in the surface of the coral in one specimen, 

 and much more distinctly, especially at the carinal extremity of the shell, in the other. 



Size of the largest specimen 10 mm. in its longest diameter, of the smallest 7 mm. 



The scutum and ter gum (PI. XXVII, fig. 2) are closely united, and even calcified 

 together in the specimen I dissected. The line of junction between the two makes a not very sharp 

 angle with the strongly curved occludent margin of the scutum. This valve is not very elongate, 

 being slightly more than twice as long as the height near the line of junction.. The scutum 

 narrows towards the rostral end, where the basal and occludent margins meet in a somewhat 

 produced angle. Along the occludent margin there is a strong ridge or ledge which bends inwards. 

 The basal margin is concave, the adductor ridge developed into a rather broad plate, which 

 projects considerably below the basal margin. 



The tergum is relatively large, its surface being hardly smaller than that of the 

 scutum-, spur well-developed, with the extremity bluntly pointed. Crests for the attachment of 

 the tergal depressor muscles distinct and projecting beyond the basal margin. 



The study of the structure of the animal contained within the shell lias yielded the 

 following results : 



Mouth. Labrum deeply and widely notched; a pair of very small triangular teeth, 

 and numerous short and stiff hairs on both sides of the notch. Pal pi stout, short and broad, 

 with the lower margin straight and the upper rounded; along the lower margin shorter 

 hairs are observable, longer ones at the tip, and very long and strongly curved hairs at and 

 near the upper margin ; the hairs at the tip are so densely disposed as to form a distinct tuft. 



Mandible with five teeth, and quite a rudimentary inferior angle terminating in a 

 group of very small, pointed teeth. The first tooth is relatively short and single, the second 

 and third teeth are distinctly doublé, teeth four and five standing close together, short, broad 

 and blunt. Hairs along the posterior margin of the inferior angle not very numerous, standing 

 close together and being relatively strong. 



Maxilla short, with the edge rather long and perfectly straight and with the upper 

 and lower margins nearly parallel. Nine spines are seen along the edge; only the two 

 superior ones are broader and slightly longer than the others; a very rudimentary notch is 

 nbserved under the two superior spines ; between the spines a number of delicate hairs 

 are seen. 



