303 
The rostrum is broad with a rounded apex. In young spec- 
imens two external longitudinal stripes very often are seen indic- 
ating that the plate, as already pointed out by Darwin (1853) in 
other species, and more especially emphasized by Pilsbry (1916), 
is in faet composed of the rostrum and two rostral latera. In old 
specimens the external sutural lines fade away because of both the 
Fig. 49. Pachylasmci scutistriata from 38° 12’ S., 149° 40 ’ E. a rostrum + rostral 
latera, external aspect, b the same plate in inside view, c external view of tergum, 
and d of scutum, e and f inside view of scutum and tergum. [All figures X 4]. 
irregular structure and the corrosion of the surface; but an ex- 
amination of the interior surface (Fig. 49 b) also now clearly reveals 
the boarders of the components: the rostral latera at first sight 
may indeed be taken as radii of the rostrum. In transverse sect- 
ions the sutures are rather easily traced all through the plate, al- 
though the connection is so strong that the suture does not gener¬ 
ally form the line of fracture, when the plate is broken to pieces. 
Probably the plates will turn out to be quite separate in smaller 
specimens than I had at hånd, in the same way as Darwin has 
observed it in other species of the genus. 
The scutum is triangular with distinet lines of growth (Fig. 
48 d). The growth zones are groved, and the groves are arranged 
in lines radiating from the apex, so that the scutum at first sight 
seems to be regularly radially striped. The interior surface is al- 
