1864,] TATE CEETACEOirS ROCKS OF lEELAND. 41 



sata is close to the flat anterior side ; in P. cordata it is at about 

 one-third of the breadth of the shell from the anterior margin. In 

 P. decussata the Innule is not defined. 



Locality. — It is not uncommon in the White Limestone (Upper 

 Chalk), at Kilcorig, Lisburn, and also at Dungiven. 



15. Pholadomta Stewaexi, spec. nov. PI. IV. fig. 2. 



Shell oblong, inequilateral; umbones prominent; length of anterior 

 side about one- third of the length of the shell ; margin rounded ; 

 posterior side truncated, with a keel proceeding from the umbo to 

 the lower posterior margin, enclosing between it and the hinge-line 

 a smooth area. Ornamented by about ten straight r.'')diating ribs, 

 which are thickened where crossed by the prominent lines of growth. 



D'miensions. — Total length 1|- inch ; height 1 inch ; length of anal 

 side Ig inch. 



Affinities and Differences. — Allied to the young oi P.Iloyana,WOvh., 

 in its form and ornamentation, but differs from it in its truncated 

 posterior margin. P. Stewarti has constantly the dimensions given. 



Locality. — One of the most common bivalves in the White Lime- 

 stone (Upper Chalk) of Lisburn, &c. 



I have much pleasure in dedicating this species to Mr. S. A. Stewart, 

 a valued friend and pupil, who has contributed much to the palaeon- 

 tology and botany of the north of Ireland. 



16. Teeebratula aeetjPta, spec. nov. PI. Y. figs. 1 a, 1 b. 



Shell elongated, oval, much longer than wide ; greatest breadth 

 at the middle, whence the shell tapers rapidly towards the front 

 and beak, marked with inequidistant concentric lines of growth and 

 faint longitudinal striae; shell- structure punctated. Yalves nearly 

 equally convex ; imperforate valve most convex near the umbonal 

 region ; ventral valve biplicated ; beak very short, prolonged and 

 transversely truncated by a circular foramen of large dimensions ; 

 beak-ridges ill defined ; deltidium inconspicuous, from the aperture 

 being contiguous to the umbo of the dorsal valve ; hinge- area re- 

 markably declinous. 



Dimensions. — Length 2 inches ; breadth ly^^- inch ; depth 1 inch. 



Affinities and Differences. — This biplicated Terebratida cannot 

 well be confounded with any of the Cretaceous species. It, how- 

 ever, resembles T. obesa and T. biplicata, from which it is readily 

 distinguished by its transversely truncated beak, which is produced 

 but very slightly beyond the plane of the umbo of the dorsal valve. 

 In both of these species the beak is incurved; the more spindle-shaped 

 appearance of T. ahrnpta is a very distinctive character. The largely 

 truncated beak and foramen contiguous to the umbo distinguish this 

 species from biplicated examples of T. longirostris, and of certain 

 Belgian Cretaceous forms, which in other respects bear some re- 

 semblance to it. 



Locality. — 1 have collected this species at Lisburn and at Moira, 

 where it is rare. Specimens in the Portlock Collection, in the 

 Museum of Practical Geology, are from Dungiven, co. Londondeny. 



