191 



THE ANATOMY AND RELATIONSHIPS OF HELIX SUBPLICATA, 



SOWERBY. 



By Professor T. D. A. Cockerell. 



(Communicated by B. B. Woodward, F.L.S.) 



Read 8lh April, 1921. 



Helix suhplicata is a fine species, of the general form of //. aspersa, 

 confined to the island of Porto Santo, one of the Madeira group. 

 It was described by G. B. Sowerby in 1824 (Zool. Journ., i, p. 56, 

 pi. 3, fig. 1) from specimens collected by Mr. T. E. Bowdich. For 

 many years it was only known as an extinct species, fossil in the sandy 

 Pleistocene deposits of Porto Santo. In the spring of 1848, however, 

 it was found alive by WoUaston and Armitage on the Ilheo de 

 Baixo, or Lime Island, the largest of the islets round Porto Santo. 

 The living specimens showed that the shell was covered with a rich 

 brown periostracum, and was wholly without bands or spots. When 

 I was recently in Porto Santo I obtained a good series of fossil 

 H. suhplicata, varying much in size, in the vicinity of the Fonte 

 d'Areia, on the main island. I visited the Lime Island and,, found, 

 one shell with the periostracum on the steep slope of the eastern side. 

 On returning to Funchal I called on the Rev. Drummond Paterson, 

 who very kindly placed at my disposal a couple of living H. suhplicata, 

 collected by Mr. Jose de Souza on the Lime Island. I was thus able 

 to examine the anatomy and fix the position of the species in the 

 classification. 



H. suhplicata crawls freely by day, and is not easily alarmed. 

 When it crav/ls the foot projects behind the shell, but the head is 

 only 2 or 3 mm. in front of the lip, instead of being far extended as 

 in H. aspersa. The animal is of a very dark plumbeous colour, 

 almost black, with oculiferous tentacles long (about 13 mm.) ; the 

 inferior tentacles are also long ; mantle grey ; foot pointed behind; 

 sole plumbeous, dilute grey in middle. There is a greater distance 

 between the lower and the oculiferous tentacles than in H. aspersa. 

 The rugse are essentially as in aspersa. The shell is peculiar, not only 

 for the strong transverse riblets, but especially for the character of the 

 apical whorls, which show, except at the extreme apex, close-set, 

 strong pustuliform granules, arranged more or less clearly in oblique 

 decussating series. In this character the shell differs conspicuously 

 from H. aspersa, as well as from H. mazzullU, Leptaxis furva, and 

 emhescens, L. phlehophora, etc. It resembles, in this peculiarity 

 of sculpture alone, the extinct Plehecula howditchiana, Fer., as well 

 as certain other shells not closely related. 



Pilsbry {Man. Conch., 2nd ser., ix, p. 309), in another connection, 

 comments on this type of sculpture thus : " A thorough study of 

 the Miocene Helices is necessary to determine whether the peculiar 

 sculpture which occurs in so many forms is a character assumed 



