APLYSIID^E. 59 



Shell (pi. 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 (pi. 15, fig. 86). 



Bay of Panama. 



Navarchus cenigmaticus BERGH, Bull. Mus. Comp. Zool., xxv, p. 

 217, pi. 10, f. 11, 12 ; pi. 11, f. 6-9 ; pi. 12, f. 8-10. 



II. 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^E 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^E with the shell spirally convoluted, Bulla-\ike, not 

 buried ; no furrow between genital apertures, and, as far as known, 

 a uniserial radula. 



Family APLYSIID^. 



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 



