ii6 



The SLibcircular shell of P. aiistralis bears on the upper somewhat convex valve a large 

 number of raised irregularly radiating ridges. Thèse ridges are not equally developed ail along, 

 but are interrupted hère and there, more particularly near the margins, and make the shell in 

 such areas almost spinous ; in worn shells the spines are reduced to simple knobs. The colour 

 of the shells is dull yellow with a large number of small black dots scattered ail over the surface. 



Distribution : P. mistralis has been recorded from the Australian Seas, the Philippines, 

 Madagascar and South Africa. 



In the "Siboga" collection there are a number of weathered shells from the Bay of Badjo, 

 West coast of Flores (St. 50), Anchorage south of Lucipara Group (St. 225 c) and Ambon 

 Anchorage (St. 231). Probably two young shells from St. 225 a, b are also to be referred to 

 this species. 



2. Plicatula c/nnensis Môrch. 



1843. Plicatida imbricata Menke, Moll. Nov. Hollandiae, p. 35. 



1847. Plicatula imbricata Sowerby (ex parte, nec Koch & Dunker), Thés. Conch., I, P/zV^/z/Za, 



p. 437, pi. XC, fig. 6, pi. XCI, figs. 15 — 17. 

 1853. Plicatula chinensis Môrch, Cat. Yoldi, II, p. 61. 

 1856. Plicatula Imbricata Manley, Rec. Biv. Shells, p. 288. 

 1873. Plicatula imbricata Sowerby (ex parte, nec Koch & Dunker), in Reeve, Conch. Icon., 



XIX, Plicatula, pi. I, figs. 4^, b, d. 

 1880. Plicatula imbricata von Martens, Mobius Beitràg. Meeresf. Mauritius, Seychell., p. 313. 

 1890. Plicatula imbricata Jousséaume, Mém. Soc. Zool. France, I, p. 223. 



1898. Plicatula imbricata Melvill & Standen, Proc. Malacol. Soc. London, III, p. 46. 



1899. Plicatula imbricata Hedley, Mem. Austral. Mus., III, pp. 492, 528. 



1899. Plicatula imbricata Melvill & Standen, Journ. Linn. Soc. London (Zool.), XXVII, p. 181. 

 1902. Plicatula imbricata Shopland, Proc. Malacol. Soc. London, V, p. 179. 



1909. Plicatula imbricata Lynge (ex parte), D. Kgl. Dansk. Vidensk. Selsk. Skr. Nat.-Math., 



(7) V, p. 152. 



1910. Plicatula imbricata Hedley, Austr. Ass. Adv. Sci., XII, p. 345. 



1916. Plicatula imbricata Hedley, Journ. Proc. Roy. Soc. W. Australia, I, p. 158. 



1919. Plicatula imbricata Odhner, Arkiv Zool., XII, n". 6, p. 4. 



1929. Plicatula imbricata Dautzenberg, Faun. Colon. Français., III, p. 558. 



Menke's name Plicahila imbricata was changed by Morch to P. chinensis ov^ing to 

 Koch & Dunker having previously described a cretaceous fossil under this name. Lynge in his 

 account of this species has suggested combining almost ail the known species of the genus under 

 one spécifie name, but he apparently did not hâve sufficient material at his disposai. 



The ovate to subcircular outline of the shell, the distantly placed angular ribs, covered 

 with short foliaceous spines are characteristic of this species. 



Distribution : — P. chinensis has a vvide range in the Indo-Pacific. 



In the "Siboga" collection it is represented by young and half grown shells from Macassar 

 (St. 71) and St. 274 (5°28'.2S., i34°53'.9E., 57 mètres). 



3. Plicatula horrida Dunker. 



1847. Plicatula imbricata Sowerby (ex parte, nec Koch & Dunker), Thés. Conch. \, Plicatida, 



p. 437, pi. XCI, fig. 18. 

 1873. Plicatula imbricata (ex parte), Sowerby in Reeve, Conch. Icon., XIX, Plicatula, pi. I, 



fig. \c. 



