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



umbo at the apex, which is produced and slightly recurved ; it projects a little over the 



tergum. 



Tergwm triangular, stout, broad. Occludent margin long, arched. Apex recurved. 

 Scutal margin almost straight, carinal margin straight in the under, hollowed out in 

 the upper, part. 



Carina very large, .simply bowed, but almost straight. Koof flat, not bordered by 

 distinct ridges. Sides of the valves at angles with the roof greater than 90°. These 

 sides are broader near the upper extremity than near the lower end. 



Upper latus quadrangular; the angle described by the scutal and basal margins 

 truncated ; hence the valve appears to be pentagonal. The apex slightly projects over 

 the scutum. 



Rostral latus quadrangular; the scutal and basal margins parallel. The valve is 

 divided by a ridge into two triangular parts. 



Infra-median latus does not reach the slightly truncated scutal-basal angle of 

 the upper latus ; narrow. Umbo at the upper extremity. 



Carinal latus quadrangular. Carinal margin almost straight, umbo seated near the 

 base and slightly protuberant ; basal, lateral, and upper margins almost straight. Beneath 

 the ridge, which runs from the umbo to the angle between the lateral and basal margins 

 of the valve, only a very small triangular part is situated. 



Length of the capitulum, 1 7 mm. 



Peduncle cylindrical, rather narrow. Length of the peduncle, 5'5 mm. Scales almost 

 totally covered by membrane, hence indistinct ; their edges only are slightly protuberant 

 beyond the surface of the peduncle. 



The structure of the animal contained within the valve has not been studied by me. 

 With regard to the complemental males of this species, the following may find a place 

 here (PI. X. fig. 6). At the interior of each scutum there is found one attached close to 

 the occludent margin, between the adductor muscle and the tergal margin. The length 

 of these complemental males is Tl mm., their breadth about 07 mm.; so their shape is a 

 broad oval. The mantle which covers them is almost smooth on one side only ; where 

 the genital apparatus opens, it is furnished with very short spines. The structure of the 

 interior is very simple ; there is a very large heart-shaped testis, which at its pointed 

 extremity communicates by a rather long duct with the receptaculum seminis. From 

 this, as in the other species, a long vas deferens is given off which opens at the posterior 

 extremity of the small body. The male is attached to the interior of the scutum by 

 means of prehensile antennse. The extremity where the genital apparatus opens forms 

 a globular excrescence, the end of which bears some stronger spines. 



Scalpellum tenue was taken at Station 146, December 29, 1873 ; lat. 46° 46' S., long. 

 45° 31' E.; depth, 1375 fathoms; bottom temperature, 1°'5 C; bottom, Globigerina 

 ooze. 



