20 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



From Pleuronmitilus falcaius, J. de C. Sowerby,^ sp., and P. suh- 

 distinctus, A. H. Foord,- from tlie Coal-measures of Shropshire, the 

 present species can be easily distinguished by the relatively greater 

 width of the cross-section of its whorls, by the character of its 

 ornaments, and by the straighter course of the peripheral portion of 

 its suture-line. 



The specimen figured as NauiiluH tetragonus by J. Phillips in his 

 " Geology of Yorkshire," pt. ii (1836), pi. xxii, fig. 34, may belong to 

 the present species, but in the absence of the original it is not possible 

 to arrive at a definite conclusion. 



The only specimens known to the writer that are properly localised 

 are from the Carboniferous rocks of Hebden Bridge, Yorkshire, where 

 they occur in the Pendleside series. 



EXPLANATION OF PLATE II. 



Fig. 1. — Lateral aspect of type-specimen in the British Museum collection (No. C. 



5277) from the Carboniferous (Pendleside Series) : probably Yorkshire. 



Is indicates the position of the last septum ; immediately above this is 



seen the band of attachment, sm being the punctated area indicating the 



position of the shell-muscle, and b the narrow band connecting the ventral 



ends of the shell-muscles. 

 ,, 2.— Peripheral aspect of the same, showing also the band of attachment close 



to the base of the body-chamber ; the lettering as in Fig. 1. 

 ,, 3. — Peripheral aspect of same, showing sculpture of the test. 

 ,, 4. — Anterior aspect of the last septal surface of the same, showing the position 



of the siphuncle («i), the lateral ventral zone (te), and the impressed 



zone [hnz). 

 ,, 5. — Lateral aspect of the nepionic and neanic portions of an example in the 



collection of Dr. Wheelton Hind. The sudden swelling at the end of 



the first half whorl indicates the end of the nepionic stage. Carboniferous 



(Pendleside Series) : Hebden Bridge, Yorkshire. 



All the fi"-ures are drawn three tmies the natural size. 



1 J. de C. Sowerby : Trans. Geol. Soc. [2], vol. v, pt. 3 (1840), expl. of pi. xl, fig. 9 



( Nniitihis falcatun) . 



2 A. H. Foord: Cat. Foss. Ceph. British Museum, pt. ii (1891), p. 139. 



