246 F. R. Cowper Heed — Salter's TJndeserihed Species. 



11. — WOODWARDIAN MuSEUM NOTES : SaLTER's UnDESCRIBED 



Species. IV. 



By F. R. Cowper Eeed, M.A., F.G.S. 



(PLATE XI.) 



GASTEEOPODA (continued). 



HoRiosTOMA DiscoRS (Sowerby), var. Mari^ (Salter MS.). (PI. XI, 



Figs. 5 and 6.) 

 1873. JEiiomphalus Marice, Salter: Cat. Camb. Sil. Foss. Woodw. Mus., p. 156 



[a 859, «860). 

 1891. Euomphalus Marice, "Woods: Cat. Type Foss. Woodw. Mus., p. 103. 



There are four specimens of this form in the Woodwardian 

 Museum, labelled a 859 and a 860 by Salter, and all come from the 

 Wenlock Limestone of Dudley. Salter (loc. cit. supra) says of it ; 

 "Eelated to E. discors, but with most regular ridges of growth, 

 A beautiful shell, dedicated to a most worthy lady — the patient 

 preparer of this collection [Mrs. Fletcher]." All four specimens 

 belong to the Fletcher Collection. 



Diagnosis. — Shell nearly discoidal ; spire short, usually low and 

 depressed ; whorls rounded, five or six in number, ornamented on 

 their apical surface by four or five weak and inconspicuous 

 longitudinal keels, which are crossed nearly at right angles by 

 prominent transverse, equidistant, and regular sharp lamellse, not 

 very closely set together, and only very slightly undulated where 

 they cross the weak keels. As they pass round to the umbilical 

 surface of the whorls they bend back gently, but again curve 

 forward to the line of contact of the whorls. The umbilical surface 

 of the whorls is devoid of longitudinal keels, except in young 

 individuals. Umbilicus deep, wide, open, exposing all the whorls. 

 Aperture not preserved. 



Measurements. 



mm. 



Breadth of one specimen (« 859) 60'0 



Approximate height of the same 20-0 



Average distance of varices on upper surface 1'5 



Breadth of specimen {a 860) showing the under surface of 



shell 64-0 



Depth of umbilicus of same 12-0 



Ebmarks. — The distinguishing feature of this form is the 

 regularity and prominence of the transverse lamellae and their 

 slight undulation in crossing the keels. Otherwise it closely 

 resembles H. discors and its varieties, including H. rugosum, 

 Sowerby.^ It does not seem possible to retain it as an independent 

 species, as it nearly approximates many specimens of this very 

 variable species H. discors, and transitional forms with intermediate 

 characters are not uncommon. 



HoRiosTOMA DISCORS (Sowcrby). 

 1873. Euomphalus pacificatus, Salter: Cat. Camb. Sil. Foss. 'Woodw. Mus., p. 156 



[a 861). 

 1891. Euomphalus pacificatus, Woods: Cat. Type Foss. Woodw. Mus., p. 103. 



1 Lindstrom : Silur. Gastrop. Pterop. Kongl. Sv. Vet. Akad. Hand!., Bd. 19, No. 6 

 (1884), pp. 157-159, pi. xvi, figs. 20-26 ; pi. xvii, figs. 1-10. 



