Jheringula paulensis, a new generic Type of Macrothricidæ. 9 



prominent, though easily observable as an elevated ridge 

 encircling the antennæ above their base, and joining the 

 carapace at the place where the free edges of the valves 

 take their origin. Seen dorsally or ventrally (PI. I, fig. 2), 

 the head appears slightly tapered and obtusely rounded in 

 front. 



As regards sculpture, the shell appears almost perfectly 

 smooth and highly pellucid, though a very faint reticulation 

 may be proved to exist, on applying a very oblique illumi- 

 nation of the microscope. 



The eye (see PI. II, fig. 1) is of moderate size, and placed 

 just in the most prominent part of the head. It is sur- 

 rounded by a very thin and hyaline capsule, and exhibits 

 numerous highly refracting crystalline cones, imbedded in 

 a dark pigment, which, however, has a coating of a some- 

 what lighter brownish colour. In the lateral view, about 8 

 crystalline cones are visible in the periphery of the eye. 

 Seen dorsally or ventrally (PI. I, fig. 2), the eye exhibits 

 traces of its original duplicity, being rather broader than it 

 is long, and having a slight sinus behind. As usual, the eye 

 is moved by the aid of 3 small muscles on each side, ori- 

 ginating close together from the inner surface of the shell. 



The accessory eye, or ocellus, occurs farther below, be- 

 tween the compound eye and the rostrum, and somewhat 

 nearer to the latter, and is very small, being imbedded 

 in a ganglionic mass. 



The antennulæ (see PI. I, figs. 1, 2, 5; PL II, fig. 1) are 

 very movably appended to the tip of the rostrum, and more 

 generally extend somewhat behind, diverging to each side 

 (see PI. I, fig. 2). They each form a slender cylindric stem 

 of about half the length of the cephalic shield, and slightly 

 bent at the base, where they exhibit a slight dilatation, carry- 



