58 DEVONIAN FAUNA. 



curve over the shoulder, and becoming slightly concave or sigmoidal at the centre 

 and widest part of the whorl, at which is situated a very elevated rounded sinus- 

 band, and below which the outline of the body- whorl passes round with a circular 

 curvature to the umbilicus. Umbilicus wide and deep. Ornament, above the 

 sinus-band, consisting of three or four equidistant, very narrow, distant, spiral 

 threads, between which alternate similar finer threads, crossed by slightly oblique 

 and sigmoidal, similar and similarly-placed transverse threads, so as to form hollow 

 squares, which become rather nodose at the corners by the intersection of the 

 threads. Sinus-band situated close to the lower suture, and bounded by two very 

 minute entire threads, between which it is very elevated and rounded, and crossed 

 by numerous close rounded ridges, which are probably again crossed by about six 

 similar spiral threads. Ornament of the body-whorl below the sinus-band very 

 similar to that above. 



Size. — Height 13 mm., width 12 mm. 



Localities. — In the Barnstaple Atheneeum is one poor specimen from Vicarage 

 Well, and one from Top Orchard; in the Museum of Practical Geology are two 

 (a specimen and a cast) from South Petherwyn, and an external cast from 

 " Marwood Beds, East of Barnstaple " ; in the Woodwardian Museum is Sowerby's 

 original type, and a fine cast from South Petherwyn, and a poor specimen from 

 Top Orchard ; in the Porter Collection a fragmentary specimen from Roborough. 



Remarks. — The above description is taken chiefly from South Petherwyn shells. 

 The figured mould from Barnstaple differs slightly from the rest. It has closer 

 and slighter transverse threads, and three subsidiary minute threads between the 

 larger spiral threads, and its sinus-elevation is sharper. There seems considerable 

 variation in height. The cast from South Petherwyn, in the Museum of Practical 

 Geology, is so like Phillips's fig. 177*, that it may be its original ; if so, that figure 

 belongs to the present species, and not to PI. victrix ^ as I formerly thought possible. 



Affinities. — PI. Hamlingii is distinguished by the section of its whorl being 

 approximately quadrangular instead of triangular, and by its sinus-band being 

 situated high on the shoulder and followed below by a broad perpendicular back, 

 on which are several distant spiral threads. 



PL minima or minuta, F. A. Romer, is a cast very similar to that represented 

 by fig. 12, and might very well belong to this species; but, as its ornament is 

 undescribed, it is impossible definitely to identify it. It occurs in the Wissenbach 

 Slates. 



PL Orhigniana, D'Arch. and de Vern,^ and its variety, PL Beaumo7iti, d'Arch. 



and de Vern.,^ are distinguished among other points by their sunken sinus-band. 



1 1891, Whidborne, ' Dev. Faun.,' vol. i, p, 301, pi. xxviii, figs. 15, 16. 

 « Ibid., p. 283, pi. xxvii, fig. 4. 



* 1842, D'Arch. and de Verneuil, ' Geol. Trans.,' ser. 2, vol. vi, pt. 2, p. 361, pi. xixiii, 

 figs. 1, 1 a. 



