APLYSIID®. 59 
Shell (pl. 14, figs. 79, 80) situated in the posterior part of hinder- 
body at the base of the tails, consisting of a chalky, white portion 
and a thin cuticular part double the width of the former. Penis as 
usual, the prostate gland T-shaped, granulose (pl. 15, fig. 86). 
Bay of Panama. 
Navarchus enigmaticus BERGH, Bull. Mus. Comp. Zool., xxv, p. 
elie pl tO. 11-02: pl. 11) f 6-9; pl. 12, f. 8-10; 

Il. TECTIBRANCHIATA ANASPIDEA. 
Tectibranchs without a fleshy head shield, the head bearing two 
or four folded or slit tentacles; shell spiral or plate-like, usually 
enclosed by the mantle, with posterior terminal nucleus; rarely ab- 
sent ; pleuropodial lobes developed. Penis near the right anterior 
tentacle, widely separated from the female orifice and vas deferens, 
which open near the gill. 
Two distantly related families compose this division : 
APLYsIID& with plate-like shell largely or wholly buried, or none ; 
a conspicuous furrow connecting the furrowed penis with the com- 
mon genital orifice; the radula multiserial. 
OXYNOEID# with the shell spirally convoluted, Bud/a-like, not 
buried ; no furrow between genital apertures, and, as far as known, 
a uniserial radula. 
Family APL YSIID. 
Animal lengthened, not protected by a shell, the neck and head 
narrower than body, mouth a vertical fissure; anterior angles of 
head produced in two tentacular lobes folded above; behind them 
the cylindric or conical rhinophores slit above, in front of which are 
the minute eyes. Epipodia or pleuropodia recurved over the back, 
forming two lateral or dorsal lobes enclosing mantle and gill. Gen- 
ital orifice within the dorsal slit, communicating by a long furrow 
with the invertable penis which is near the anterior right tentacle. 
Shell nearly or entirely covered by the mantle, uncoiled, in the 
form of a concave plate, sometimes absent. Mouth with corneous 
jaws and a large multiserial radula composed of similar teeth ; 
- stomach armed with cartilaginous nodules ; anus behind the gill. 
Rather large animals of flabby consistency, remarkable for the 
four large ear-like tentacles and high back, which have earned for 
