8 LEPIDOPLEURUS. 



also the girdle is very thin, narrow, and sparsely set with small pel- 

 lucid spicules near the margin. The posterior mucro or apex of 

 the posterior plate, in belknapi, is prominent, overhangs a shallow 

 concavity and from its point there diverge anteriorly four depressed 

 lines, the outer two to the anterior lateral angles of the plate, the 

 inner two equidistant from each other and the outer lines. Between 

 these lines the plate is swelled, forming three rounded ridges, 

 extending forward like the leaflets of a trefoil or clover. Nothing 

 resembling this has been observed on any of the other species which 

 have come under my notice. The soft parts in spirits appear to 

 resemble the other species compared with it. It is evidently adult. 

 (DalL) 



The figures represent the form dredged by the 'Challenger' off 

 Luzon, Philippines. Haddon describes these specimens as follows : 



Shell. Brittle, closely covered with large, round, smooth tuber- 

 cles. The sides meet at an angle of about 110. Sutural laminse 

 small. 



Anterior valve. With a few irregular lines of growth, thickly 

 covered with irregularly disposed tubercles. 



Intermediate valves. Central areas : with a shallow depression 

 on each side of the median ridge, which gives the latter a pinched 

 appearance ; this depression is most apparent at the hinder border 

 of each valve. The tubercles have a general arrangement in 

 oblique lines radiating forwards from the keel and at the same time 

 in lines concentric to the umbo, but these two series of lines are not 

 always regular, and the tubercles often appear to be irregularly dis- 

 posed. A series of short concentric rows usually demarcate the 

 anterior border of the lateral areas. Lateral areas : scarcely ap- 

 parent ; a groove indicating a line of growth occurs at a short dis- 

 tance from the girdle ; tubercles irregularly disposed, with a ten- 

 dency, however, to concentric lines. 



Posterior valve. With a small subcentral umbo, behind which 

 is a slight depression. Anterior area: the lateral longitudi- 

 nal depression causes the jugum to be slightly prominent and thus 

 gives the anterior area a somewhat trilobed appearance; the tuber- 

 cles radiate from the rounded keel. Posterior area; with concen- 

 tric lines of growth and closely set tubercles. 



Girdle. Narrow, thickly covered with delicate small oval scales ; 

 longer, narrower and more pointed scales occur along the border 

 and in the angles between the valves. 



