84 THE VOYAGE OF H.M.S. CHALLENGER. 



This is a very characteristic species, a dozen specimens of which were collected by 



the Challenger. 



The capitulum consists of fourteen valves, and is robust; without the carina it has 

 the shape of a parallelogram, hence the name which I propose for it. It has a consider- 

 able thickness at the lower end, but grows more compressed towards the upper end. The 

 capitulum is covered by a strongly adhering yellowish chitinous membrane. The lines of 

 growth are not very distinct. 



Scutum more than twice as long as broad, trapeziform, the occludent and the lateral 

 margins being parallel to each other. The umbo is situated at the apex, which slightly 

 projects over the tergum ; tergal margin slightly hollowed out. At the angle which the 

 tergal margin describes with the lateral margin, a small projection is formed. The basal 

 margin is straight. 



Tergum triangular, flat, with a short and slightly arched occludent margin. Apex a 

 little recurved, basal angle pointed. The area covered by the tergum smaller than that 

 covered by the scutum. 



Carina simply bowed, with a flat roof, increasing considerably in breadth from the 

 upper to the lower end. On each side the roof is bordered by a strong ridge. Sides nearly 

 at right angles with the roof, of equal breadth over its whole length, only growing 

 narrower at the lower extremity. 



Upper lotus quadrant-shaped, with a not very deep notch cut out of the basal 

 margin, which notch receives the upper margin of the carina! latus. 



Rostrum minute, hour-glass shaped, the upper part being quadrangular, the lower being 

 elongated-triangular; inserted like a wedge between the umbones of the rostral latera, 

 so as to be easily overlooked. 



Rostral latus quadrangular, the basal margin with a projecting ridge and slightly rounded. 

 Infra-median latus triangular and large. The under part on both sides is furnished 

 with a kind of ala ; the middle and under part formed by the inferior angle of the tri- 

 angle projects considerably beyond the surface of the capitulum. 



Carinal latus elongated, appears as if formed of two valves united together, both of a 

 triangular shape with slightly curved sides. The umbo of the carinal latus projects very 

 much beyond the line of the carina and also beyond the surface of the capitulum. 

 Length of the capitulum, about 21 mm. 



Peduncle short (4 mm. in a specimen of 21 mm.), cylindrical, of the same width over 

 its whole length, almost entirely smooth, at least not furnished with calcareous scales as in 

 the other species. 



Mouth. — Labrum with the upper and anterior part very bullate. Palpi small, almost 

 triangular, not very slender. Mandibles (PI. IX. fig. 1) with three teeth, the second and 

 third smaller than the first. Inferior angle broad, pectinated. Maxillce (PL IX. fig. 2) 

 with a very deep notch behind the upper great spines, and about seven pairs of rather 



