144 DEVONIAN FAUNA. 



above each side of umbo, subtriangular. Hinge-margin less than half the length 

 of the shell, with two deep internal ridges extending obliquely downwards three 

 quarters of its length. Margins subcircular. Contour flat, the umbonal area 

 being defined in front by a slightly curved line, and behind by a strong straight 

 depression, extending to the centre of the posterior margin. Surface (?). 



Size. — Height 16 mm., length 16 mm. 



Locality. — One specimen from Top Orchard is in the Barnstaple Athenasum. 



Remarks. — The only specimen of this shell with which I am at present 

 acquainted is so indistinct that I at first omitted it from the plates, but further 

 examination convinced me that it has protruding wings in the style of Amussium, 

 and is therefore generically distinct from the other specimens with which I 

 supposed it associated. These wings are lower and rounder than is usual in the 

 species that have been referred to the genus EntoMum, and its slightly inequilateral 

 shape seems to distinguish it from most of the Belgian Carboniferous forms. 



I am not aware that any other species of the genus has hitherto been described 

 from Devonian rocks. 



4. Pkothyris, 1 sp. Plate XVII, fig. 6. 



Description. — Shell moderate in size, ensiform, very elongate, its length being 

 about three times its height. Anterior margin apparently rounded and notched. 

 Inferior margin very long and straight, and nearly parallel to the upper margin, 

 the shell being slightly higher in front than behind. Posterior margin apparently 

 gaping. Umbo low, rounded, situated at or about the anterior fifth of the shell. 

 Surface marked with rather few close, low, rounded growth-lines, most visible in 

 the marginal half, and with eight or ten rather strong, unequally distant, linear, 

 oblique, impressed rays running from behind the umbo to the posterior fourth of 

 the inferior margin. Post-cardinal slope apparently narrow, flat, oblique, and 

 marked by a few much stronger radiating ridges. 



Size. — Height 10 mm., length 30 mm. 



Locality. — Two specimens are in my Collection from Sloly Quarry. 



Remarks. — These specimens are interesting from the clearness of their peculiar 

 ornament. They are too imperfect for identification, but one of them appears to 

 show the characteristic notch of the genus, though in a much-injured condition. 

 Both in size, shape, and ornament they seem so different from either of the 

 species described above that I think they will prove distinct from any of them. 



1 See page 86. 



