206 On new Mollusca from Aden. 



but possessing- essential characters of its own. The shell is 

 equilateral, equivalve, almost round ; umbones slightly 

 oblique ; surface of a dull drab colour, here and there relieved 

 by bright brown spots or blotches, with about twenty-four 

 closely grained or scaly costse; these ribs are rather broad for 

 the size of the shell, and the interstices are narrow, very 

 rudely spirally scaled in a similar way to the ribs. The 

 hinge-teeth are whitish, about thirty in number ; the interior 

 is whitish, spotted and stained in places with rufous brown. 



Thracia adenensis^ sp. n. 

 (PI. XII. fig. 16.) 



T. testa trapezoide, albida, papj'racea, tenui, concentrioe irregulariter 

 striata, parum nitida ; umbonibus prominulis; valva dextrasinistrse 

 marginem ventralem superimpendeiite, majore et coiivexiore, ab 

 umbonibus ad extremitatem marginis veutralis posticam unicari- 

 nati I, sinistra simili carina prajdita ; pagina interna albo-lactea, 

 baud nitida, laevi ; cicatrice anteriore oblonga, postica squarrosa, 

 latiore, sinu palliali profundo. 



Long. 28, alt. 19, diam. 8 mm, 



A pure white papyraceous shell, extremely truncate poste- 

 riorly, with conspicuous un)bones, that ot the right valve 

 superimpending its fellow, just as the right ventral margin 

 overhangs that of the left. The right valve is more convex, 

 but the left is not so flattened as in some Thracice ; a con- 

 spicuous oblique keel in both valves extends from the umbones 

 to the lower posterior margin. 



EXPLANATION OF PLATE XII. 



Fig, 1. Nassa {Hebra) jwlychroma. 



Fig. 2. Mangilia {Glyphostomd) fenesf.rata. 



Fig. 3. CoralliopMla urahica. 



Fig. 4. Aclis excereta. 



Fig. 5. Eulima SJioplandi. 



Fig. 6. Leiostraca constellata. 



Fig. 7. Leptothyra yemenensis. 



Fig. 8. Calyptrcea (Galertis) Edgariana. 



Fig, 9. Novaculina xyreces. 



Fig. 10. Tellina (Tel/inella) manumissa 



Fig. 11. Tellina {Angulus) yemenensis. 



Fig. 12. Gari amianta. 



Fig. 13. Petricola lyra. 



Fig. 14. Semele Shojjlandi. 



Fig, 15. Pectuncubis tegulicius. 



Fig. 16. Thracia adenensis. 



