M THE VOYAGE OF H.M.S. CHALLENGES. 



sented by a single full-grown specimen only. Though with hesitation, I refer also to it 

 three other specimens taken at two different Stations. 



The capitulum consists of thirteen valves. Between the two rostral sides of the 

 rostral latera an extremely narrow calcareous streak is observed, which no doubt repre- 

 sents the rostrum, but which can hardly he said to be distinctly visible. In the largest 



cimeu the surface is almost entirely naked ; in the specimen which comes next in size, 

 the surface is covered by a membrane richly furnished with woolly hairs. The smaller 

 specimens from Station 1G9 are also hairy. As the shape of the valves, and especially the 

 high development of the valves of the lower whorl, is the same in all these specimens, I 

 feel inclined to consider the difference in hairiness as due to difference in age. 



The scutum is large, quadrilateral, twice as long as broad. The lateral margin is 

 straight, the basal margin slightly arched, the tergal margin straight, and has near the 

 convex occludent margin a small triangular projection over the tergum. The umbo is at 

 the apex. The lines of growth have two directions, and meet in a curved line running 

 from the apex to the angle formed by the basal and lateral margins. The stride are almost 

 at right angles to the lines of growth. 



The tergum is triangular, flat, large, with the three margins almost entirely straight ; 

 the carinal margin is the only one which makes an exception, as it is slightly convex in 

 the undermost and slightly hollowed out in the uppermost half of its length. The striae 

 are diverging from the apex to the scutal margin ; the lines of growth run parallel to the 

 scutal margin. The umbo is at the apex. 



The carina is simply bowed, with the umbo at the apex, and the roof deeply furrowed 

 and bordered by strongly-developed lateral ridges. The roof increases considerably in 

 width from the upper to the lower end ; the two sides are flat and at right angles with 

 the roof, they have the same width over their whole length. 



The upper lotus has the form of a trapezium, the carinal margin being almost exactly 

 parallel with the scutal margin. The latter is three times as long as the former. The 

 tergal margin has the same length as the basal margin. All the margins are straight and 

 the umbo is at the apex. The lines of growth in the one part run parallel with the basal, 

 and in the other parallel with the carinal margin. 



The rostrum is not distinct. 



The rostral lotus is — when seen laterally — triangular; its real shape, however, is 

 rather trapeziform. The umbo is at the rostral extremity, where the valve projects over 

 the base of the scutum. The scutal margin is the prolongation of the basal margin of 

 the upper latus. The hind margin is convex, and imperceptibly passes over into the 

 short basal margin. 



The infra-median lotus is triangular, with the umbo situated at the apex, and the 

 basal margin broad. The rostral and carinal margins are slightly hollowed out. 



The carinal latus is very large, with the umbo seated at the basal outer angle ; the 



