REPORT ON THE LAMELLIBRANCHIATA. 315 



Lengtli 7^ mm., height 6f. 



Habitat. — Station 78, east of the Azores, at a depth of 1000 fiithoms ; volcanic mud. 



This species, although bearing a general resemblance to Amiissium lucidum, differs 

 (judging from the only two valves known) in being proportionally shorter from the beaks 

 to the ventral outline, in comparison with the transverse diameter. Its hinge-line is 

 longer, the apical angle of the beaks less acute, the left valve is radiately Urate instead 

 of concentrically striate, the anterior ear in the same valve is quite distinct in form, and 

 the internal lirse are more slender and fewer than in the Azorean examples of Amussium 

 lucidum. 



Amitssium cancellatum, n. sp. (PI. XXIII. figs. 8-8c). 



Testa compressa, parum pellucida, albida, hand polita, sequilateralis, rotundata, paulo 

 insequivalvis, valvis diverse sculptis. Valva dextra profuudior, liris tenuissimis 

 radiantibus numerosis aliisque gracilioribus confertioribus concinne canceUata, sinistra 

 concentrice sulcata, sulcis regularibus, tenuibus, sensim accrescentibus. Auriculae 

 insequales, posticis majoribus. Umbones acuti, lateribus convergentibus leviter con- 

 cavis. Linea cardinis brevis, recta, fossa mediana ligamenti parva instructa. Pagina 

 interna nitens, liris mediocriter fortibus circe 12 (aliis minoribus ssepe interpositis) 

 munita. 



This species is as a rule a trifle longer from the beaks to the lower margin than from 

 side to side. It is compressed, slightly inequivalve, only a little transparent, whitish, 

 hardly at aU glossy, and has the valves diflerently sculptured. The right or somewhat 

 deeper valve is ornamented with numerous fine thread-like radiating lirse, which are 

 crossed by still finer concentric ones. The former are more slender and closer together 

 down each side than towards the middle of the valve, and the latter, besides being finer 

 than the radiating lirse, are also much more approximated to one another, those near the 

 beaks being further apart than the rest. The left valve has somewhat of a silky 

 appearance, and is finely and closely concentrically lirate, the lirse gradually becoming 

 thicker and more remote with the growth of the shell. The auricles are small, somewhat 

 unequal, the posterior being rather larger than the anterior. They are sculptured with 

 fine lines of growth and sometimes denticulate at the top. The posterior end of the left 

 valve is sinuated below, and is separated from the main part of the valve by a deepish 

 groove, in which a slender ridge runs parallel with the dorsal slope. The beaks are small, 

 acute, the slightly concave sides converging to an angle of about 117 degrees. The glossy 

 interior of the valves is strengthened with numerous white fairly strong radiating lir^e, 

 visible exteriorly, especially in the right valve, which is a little more transparent than the 

 left. They are about twelve in number, somewhat thickened towards the outer extremities, 



