99 



The capitulum is flat with the carinal side slightly and the occludent side strongly 

 arched. It is covered by a thin membrane, which bears short hairs along the carina, forming 

 tufts at the base of that valve and in a less degree at the apex. The carina is separated 

 from the other valves by a distinct chitinous interspace. The valves of the lower whorl are less 

 than medium-sized. 



The scutum is quadrilateral and more than twice as long as broad. It has an arched 

 occludent margin ; its tergal margin is short ; its lateral margin slightly hollowed out in the 

 upper part and strongly convex in the lower. The apex is pointed, but not produced. Growth 

 ridges indicated, but not distinct. 



The ter gum is large, triangular, with the occludent margin straight. It meets the carinal 

 margin in a very slightly produced little point. The carinal margin is straight in the upper, 

 feebly convex in the under part. Ridges of growth very indistinct. 



The carina is simply and not strongly bowed. The roof is flat, increasing in width 

 from the apex downwards, bordered by ridges. The lateral parts rather narrow and having 

 about the same width over the whole Iength. 



The upper latus is large and has a somewhat irregular shape. Its umbo is at the 

 apex which penetrates into the corner between the scutum and the tergum. It has a long scutal 

 margin, slightly convex in the upper and strongly hollowed out in the under part. The carinal 

 margin is short; the lines of growth are rather indistinct. 



The rostrum (fig. 3a) is very small and triangular; it is placed in the corner between 

 the tips of the rostral latera and the scuta. 



The rostral latus quadrilateral, rather small, as is also the case with the other valves 

 of the lower whorl. 



The infra- media n latus very narrow, with the umbo at the apex, very slightly 

 increasing in width downwards. 



The carinal latus has the umbo near the base. It can hardly be said to project 

 beyond the line of the carina. The upper part is triangular and fits into the angle between the 

 carina and carinal latus. 



The peduncle is short, broader in the upper part. The scales are broad and narrow: 

 they are irregularly distributed over the surface. 



Size. The total Iength of the animal is 9 mm., that of the capitulum 7,5 mm. 



The only specimen is attached to a small stick or rod, the nature of which I cannot 



make out. It was taken by H. M. S. "Siboga" at: 



Stat. 295. January 24, 1900. Lat. io°35'.6S., Long. i24°u'.7E. Depth 2050 m. Bottom: fine 

 grey mud. 



Observation. This deep-sea form comes nearest to the species I describe on p. 105 



as Sc. gracile. I consider the two forms as different not so much because a rostrum is present 



in the one and wanting in the other species, but especially because the valves of the lower 



whorl are much more developed in Sc. gracile than is the case in the present species. The 



carinal margin of the carinal latus is moreover slightly more hollowed out in Sc. arcitatum than 



in Sc. gracile. 



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