172 DEVONIAN FAUNA. 



4. PRODTJCTUS INTERRUPTUS, Soioerby, sp. ? Plate XXII, figs. 1 3. 



? 1840. LEPT^NA INTEBEUPTA, Sowerby. Geol. Trans., ser. 2, vol. v, pt. 3, pi. Ivi, 



fig. 7. 



? 1841. n. sp. ? Phillips. Pal. Foss., p. 229, pi. Iviii, fig. 98. 



? 1844. PBODUCTA INTERIITJPTA, M'Coy. Synops. Carb. Foss. Irel., p. 110. 

 P1865. PBOJJUCTUS, pp., Davidson. Brit. Foss. Brach., vol. iii, p. 103, pi. xx, fig. 8. 



Description. Ventral valve small, very gibbose, approximately hemispherical. 

 Umbo small, flattened, not prominent, incurving to the hinge-line. Ears 

 apparently small. Ribs numerous, low, rounded, more or less distinct, occa- 

 sionally divaricating, much interrupted in the umbonal region by a number of deep 

 irregular concentric grooves (which are bounded by ridges) and crossed, especially 

 in the marginal parts, by very numerous, regular, minute, impressed threads. 

 Dorsal valve apparently concave, following the contour of the ventral valve, 

 indistinctly ribbed, and transversely ridged or wrinkled throughout. 



Size. Length 13 mm., width 11 mm. 



Localities. Six slabs (three of which are from Fremington) containing several 

 specimens are in the Porter Collection. Two specimens from Ashford Strand, 

 one from Fremington and one from Newport near Barnstaple, are in Mr. E. F. Gr. 

 Bryan's Collection. 



Remarks. This small species has the appearance of being very distinct, but 

 our specimens are all more or less imperfect and in poor condition. The shell 

 seems to be papyraceous. The strong irregular grooves, followed by blunt 

 ridges, which are chiefly seen in the central portions of the shell, break up the 

 ribs into short series in a manner which presents great likeness to P. fimbriatus, 

 Martin, 1 so that it is not impossible that it may prove to be an extreme variety of that 

 species. At the same time in our shells these grooves seem much narrower, so as 

 to cause less extensive interruption to the ribs, and at least in the ventral valve 

 they are only seen in the posterior part of the shell, the ribs being continuous 

 for the marginal half of their length. The umbo, moreover, seems much smaller 

 and depressed, and no spines are now visible upon the ribs. It is probable, 

 therefore, that they are distinct. 



Leptssna interrupter Sowerby, is a shell from the Limestone of Plymouth. 

 Its type is in the Museum of the Geological Society. It was said by Davidson to 

 " appear exceedingly like a small example of the Carboniferous P. fimbriatus, 

 Sowerby, or P. laxispinus (i.e.. P. laciniatus ?) , M'Coy, which may have got 

 accidentally mixed up among Rev. W. Y. Hennah's Plymouth specimens." Its only 



1 1861, Davidson, * Brit. Foss. Brach.,' vol. ii, pt. 5, p. 171, pi. xxxiii, figs. 1215 ; and pi. xliv, 

 fig. 15. 



