EL SS eee —_———— 
“; 
247 
the tergum between the specimens from the different stations, there could be no doubt that 
they belonged to the same species. 
The shell is white and covered by a greyish membrane with a velvety surface. This 
membrane is quite persistent round the basal part of the shell, the surface round the orifice being 
almost quite bare. The orifice is large, of a pentagonal shape; it is toothed in consequence 
of the oblique summits of the alae. This is more distinctly the case in the specimen of cylin- 
drical shape from Station 105. The oblique summits of the alae are delicately crenated, their 
surface is horizontally striated. The carina and the carino-lateral compartment have the alae, in 
the cylindrical specimen especially, very broad at the summit. The ala of the lateral compartment 
is also of a triangular shape, but it is much narrower in the upper part. The rostrum has 
neither radii nor alae; it is of a triangular shape, bluntly pointed at the tip, broad at the basis 
and very broad in the specimens from Stations 59 and 251. The outer surface of all the 
Fig. 1. Outer view of the valves Fig. 2. Inner view of the valves 
of Hexelasma velutinum gen. et spec. nov. of Hexelasma velutinum gen. et spec.@mov. 
RO, Rostrum; CA, Carina; LA, Lateral; RO, Rostrum; C4, Carina; ZA, Lateral; 
CL, Carino-lateral compartment. CZ, Carino-lateral compartment. 
valves is striated horizontally, the striae being more distinct on the rostrum and the carina 
than on the lateral compartments. On the inner surface the compartments show very delicate 
longitudinal lines, but these are not to be confounded with longitudinal ribs or septa, of which 
there is no trace. The sheath of the rostrum (PI: XXVI, fig. 6) is developed in the middle 
of the valve only, the part of the valve on each side of it being slightly excavated for the 
reception of the alae of the rostro-lateral compartments. The compartments seem to hang 
together in a very loose way: on manipulating a specimen it easily falls to pieces. The basis 
is membranous. 
With the aid of the specimen from Station 59, I was enabled to study the shape of 
the different valves more in detail. The accompanying figures show these, 4 times enlarged. 
1g 
