I 12 



1836. Spondylus ducalis Deshayes in Lamarck, Anim. sans Vertèb., VII, p. 189. 



1840. Spondylus ducalis Pfeiffer, Krit. Reg., p. 6^. 



1841. Spondylus ducalis Reeve, Conch. Syst., I, p. 165, pi. CXVII, fig. 4. 

 1843. Spondylus ducalis Chenu, lUustr. ConchylioL, p. 4, pi. VIII, figs. 2, 3, 3a. 

 1845. Spotidylus ducalis Catlovv & Reeve, Conch. Nomencl., p. 85. 



1847. Spondylus ducalis Sowerby, Thés. Conch., I, p. 426, pi. LXXXV, fig. 16. 



1853. Spondylus ducalis M()rch, Cat. Yoldi, II, p. 60. 



1855. Spondylus ducalis Berge, .Conchylienbuch, p. 97. 



1856. Spondylus ducalis Reeve, Conch. Icon., IX, Spondylus, pi. VII, fig. 26. 

 1856. Spondylus Ducalis Hanley, Rec. Biv. Shells, p. 291. 



1858. Spondylus ducalis Kùster in Martini-Chemn. Conch-Cab. (N. F.), VII (2), Pectinacea, p. 9, 



pi. III, figs. I, 2. 

 1858. Spondylus ducalis Adams, H. & A., Gen. Rec. MolL, II, p. 560. 

 1860. Spondylus ducalis Reeve, Elem. Conch., II, p. 54. 



1862. Spondylus ducalis Chenu, Man. ConchylioL, II, p. 192, figs. 972, 973. 

 1869. Spondylus ducalis Dunker, Cat. Mus. Godefi'roy, IV, p. 116. 

 1869. Spondylus ducalis Frauenfeld, Verhandl. Zool.-Bot. Ges. Wien, XIX, p. Zij . 

 1869. Spondylus ducalis Lischke, Japan. Meeresconch., I, p. 171. 

 1871. Spondylus ducalis Lischke, Japan. Meeresconch., II, p. 160. 

 1878. Spondylus ducalis Kobelt, Illustr. Conchylienbuch, p. 375. 

 1881. Spondylus ducalis de Rochebrune, Bull. Soc. Philomat. Paris, (7) V, p. 4. 



1889. Spondylus ducalis Crosse & Fischer, Journ. ConchylioL, XXXVII, p. 291. 



1890. Spondylus ducalis Paetel, Cat. Conch. Samm., III, p. 239. 



1891. Spondylus ducalis Fischer, P., Bull. Soc. Nat. Hist. d'Autun, IV, p. 208. 



1896. Spondylus ducalis Casto de Elera, Cat. Sist. Filip., p. 812. 



1897. Spondylus ducalis Sowerby, Mar. Shells S. Africa, p. 28. 



1905. Spondylus ducalis Hidalgo, Cat. Filip., p. 383. 



1906. Spondylus ducalis Owston, Japan. Loochooan Shells, p. 35. 



1910. Spondylus ducalis Dautzenberg, Journ. ConchylioL, LVIII, p. 30. 



191 1. Spondylus ducalis Pelseneer, "Siboga" Lamellibranches (Anat.), p. 32. 

 1915. Spondylus ducalis Fulton, Journ. Conch., XIV, p. 337. 



1925. Spondylus ducalis Oostingh, Geol. Comm. Agr. Univ. Wageningen, N" 9, p. 259. 

 1928. Spondylus ducalis Faustino, Summary Philippine Mar. Freshw. Mollusks, p. 34. 



As I hâve suggested in my remarks on Spondylus hystrix var. ocellatus there is some 

 difficulty in separating 5. ducalis from other closely allied forms. I hâve some doubts whether 

 S. lamarcki Chenu (loc. cit., p. 6, pL IX, fig^s. 3, 3 a, 4, 4a) is also not based on worn and 

 aged spécimens of ducalis. 



The shell of 5". ducalis is triangularly ovate, and the surface sculpture consists of closely 

 set and fairly deep radial striations. In addition there are about 10 ribs bearing large, flattened 

 scales. The interspaces between the ribs are as broad or broader than the ridges themselves. 

 In older shells the foliaceous scales are often lost and the shell surface has only the raised 

 ridges alternating with the close set ribs ; the form of the shells at this stage is, as Reeve noted 

 in the case of S. lamarcki.^ more Pecten-like. Reeve's distinction of S. ducalis of "the contrast 

 of the rows of white scales upon the blue grey ground of the interstices" is applicable to young 

 and fresh spécimens only. 



Distribution : — S. dticalis appears to be w^idely spread in the Indo-Pacific. 



The "Siboga" Expédition obtained mostly dead shells from the Kur and Roma reefs, 

 Pulu Kaniungan Ketjil (St. 89), Sanana Bay, East coast of Sula Besi (St. 193), Saleyer (St. 213) 

 and Tuai Anchorage, Kei Islands (St. 1^58). 



