18 Gr. 0. SARS. [No. 7. 



trally (fig. 2). exhibits a rather tumid form, rapidly tapering, 

 however, posteriorly to an obtuse point. 



The free edges of the valves are strongly inflexed inferiorly 

 and fringed with delicate ciliated setae, that rarely however pro- 

 ject beyond the carapace seen laterally. The inflected edge ap- 

 pears in this aspect of the animal as a slightly sinuated line 

 running along at some distance within the inferior margin (see 

 fig. 1). The dorsal edge of the carapace is smooth, except in 

 its most posterior part, where a dense armature occurs of rather 

 strong appressed denticles, continued to the tip of the posterior 

 projection. As regards the sculpture of the shell, it is that char- 

 acteristic of the genus, viz., a dense and somewhat irregular 

 transverse striation, the striae running obliquely backwards, pa- 

 rallel to the posterior edge, often anastomosing with each other, 

 and forming somewhere a dense reticulation. 



The eye, located within the most prominent anterior part of 

 the head, is rather small, with a limited number of crystalline 

 lenses, imbedded in a dark brownish pigment. When the animal 

 is viewed from above or below (fig. 2), this organ clearly shows 

 its original duplicity, being deeply incised both anteriorly and 

 posteriorly. 



The ocellus is located behind the eye. at some distance from 

 the base of the rostrum; it is very small, well-nigh punctiform, 

 but exhibits under a strong magnifier a somewhat rhomboidal 

 form, similar to that in the European species S. exspinosus. 



The antennulae, originating immediately posterior to the ro- 

 stral projection, are of conical form and tipped with very short 

 sensory filaments; to a knobshaped prominence on their anterior 

 edge, at some distance from the base, a rather elongate, anteri- 

 orly pointing bristle is affixed. The outer part of the antennul* 

 is generally covered at the sides by the anterior part of the 

 valves. 



The antennae are comparatively short, but rather powerful. 

 The scape is cylindrical in form, though somewhat thicker at 

 the base, where it is furnished with a number of circular folds- 

 It bears at the extremity, between the insertion of the branches. 



