262 Mr. J. Gwyn Jeffreys on the Mollusca of St. Helena. 



Fig. 2. Outline of a scale of Platijsomus rotundus, considerably enlarged. 



Fig. 3. Outline of a scale of Platysomus Forsteri, enlarged. 



Fig. 4. Outline of a mandibular ramus of Cfelacanthus lepturus, sligbtly 

 enlarged : a, articular piece ; b, glenoid surface ; c, dentary 

 bone ; d, teeth. The articular piece and dentary bone are laid 

 together in their natural positions, but not united ; so that the 

 form and extent of each can be distinctly traced. 



Plate XVIII. 



Fig. 1. Scale, natural size, of Cienodus (first species) : a, anterior margin ; 

 b, posterior or exposed ditto ; c, marginal border ; d, rupture 

 exposing cast of upper surface ; e, central area. 



Fig, 2. Scale, natural size, of Ctenodus (second species) : a, anterior 

 margin ; b, posterior extremity ; c, mai'ginal border ; d, central 

 area : the dotted line indicates the form and extent of the scale. 



^UNll.— The Mollusca of St. Helena. 

 By J. Gwyn Jeffreys, F.R.S. 



With the assistance of my friend Mr. M'Andrew, I have ex- 

 amined a collection of shells made by Mr. J. C. Melliss at 

 St. Helena ; and I subjoin a list of them. Most of the marine 

 shells were picked up on the beach, and are consequently in 

 bad condition. The only specimen procured from deepish 

 water (about fifty fathoms) is Ostrea crista- galli ; and this is 

 covered with two kinds of stony coral, which Prof. Duncan 

 refers to Sclerohelia Mrtella and a species of Balanophyllia. 

 The land-shells of St. Helena have been already noticed by 

 the late Mr. G. B. Sowerby in the Appendix to Mr. Darwin's 

 work on A^olcanic Islands, as well as by Mr. Blofeld and the 

 late Prof. E. Forbes in the Quarterly Journal of the Geolo- 

 gical Society of London for August 1852. In the opinion of 

 the last-named author, " a closer geographical relationship 

 between the African and American continents than now main- 

 tains is dimly indicated " by the marine mollusks of St. Helena; 

 and "the information we have obtained respecting the extinct 

 and existing terrestrial mollusks of this isolated fragment of 

 land would seem to point in the same direction, and assuredly 

 to indicate a closer geographical alliance between St. Helena 

 and the west [?east] coasts of South America than now holds." 

 And in the Report of the British Association for 1851 will be 

 found an abstract of a paper by the same distinguished natu- 

 ralist, entitled, " On some Indications of the Molluscous Fauna 

 of the Azores and St. Helena." It is here stated that "the 

 marine mollusks [of St. Helena] would seem to point to the 

 submergence of a tract of land probably linking Africa and 



