Boone, Mollusca, Cruises of "Ara" and "Alva" 293 



in which the well-separated eyes occur. There are eight to nine 

 eyes per line, in the median central area, corresponding to the same 

 number of imbricated squamae and so arranged that the eye is 

 placed in the wider, interstitial area, between the narrowed apices 

 of the elevated squamae, so that the eyes form approximate series, 

 arranged in concentric semicircles, alternating with similar con- 

 centric series of separated squamae. In the lateral area the 

 squamae on the outer half are thickened and arranged in ridges 

 longitudinal with the animal, more prominent and somewhat tend- 

 ing toward an angle with the radiating series. There are eight 

 slits present. 



Intermediate valves: In specimen A, the dorsal or jugal area 

 of the anterior two-fifths is imbricated, and of the posterior three- 

 fifths of the first intermediate valve and of the entire jugum of 

 the remaining intermediate valves is a smooth, white ridge, micro- 

 scopically punctate, with the squamae entirely fused, while in 

 specimen B, the ridge is present, but less complete, the squamae 

 imperfectly fused; on these the first intermediate valve being 

 scarcely differentiated from those of the adjacent pleural regions, 

 except on and near the beak. In both specimens the intermediate 

 valves are moderately beaked, the apices being in the mid-posterior 

 region. The pleural areas are decorated by lines of imbricated 

 squamae, A in shape, like those of the anterior valve, but ar- 

 ranged on the intermediate valves in approximate longitudinal 

 series and alternating, as on the anterior valve, in alternation with 

 grooves in which the eyes are more sparsely distributed. Immedi- 

 ately posterior to the diagonal line the eyes are very numerous, 

 being more closely spaced and covering a narrowed, triangular 

 portion of the lateral area, the apex of which ocular triangle is 

 near the beak and is one eye wide on the second valve, becoming 

 four eyes wide distally ; on valves three, four, five, six and seven, 

 the ocular triangle begins as one eye wide at the apex, widens 

 medially to three eyes wide and distally to five to six eyes wide 

 along the outer margin. The squamae between the eyes are pres- 

 ent but subdued, while on the remainder, or posterior portion of 

 the respective lateral areas, the squamae are coarse, arranged in 

 somewhat radiating series from the beak outward with the dis- 

 tinct one alternating grooves nearly devoid of eyes. The diagonal 

 line is ridge-like, composed of these prominent, imbricate squamae. 

 There is one slit present to each intermediate valve. 



