26 ORDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



South of Llangollen ; Llwyn-yr-liych, Beddgelert ; near Llanfyllin ; Hope Bowdler, 

 Shropshire. 



4. Cyrtolites nodosus, var. llandoveriana, nov. Plate V, figs, 3 — 6. 



Varietal Characters. — Shell of about three whorls in contact but scarcely over- 

 lapping, the outer one rapidly increasing in size to moutli, bluntly carinated, 

 somewhat higher than wide, broadly lanceolate to subcordiform in cross-section, 

 with obtuse umbilical edge at less than half height of whorl. Uml^ilicus open, 

 deep, exposing all the inner whorls ; umbilical slope smooth, without ribs, rather 

 steep. Upper portion of sides of outer whorl ornamented with regular strong 

 subangular transverse slightly oblique and very weakly-arched ribs, set at equal 

 distances apart, separated by gently concave wide interspaces and nearly or quite 

 meeting the corresponding ril)s of the opposite side (without any bending back) 

 on the carina. Mouth bell-shaped with margins slightly and suddenly everted. 



Dimensions. — i ii 



Height of shell . . . .13 mm. . 25 mm. 



Height of outer whorl at mouth . 7 ,, . 14 „ 



Horizon. — Lower Llandovery, 



Localities. — Blaen-y-cwm, Nantyr, Glyn Ceiriog [28050 — 52] ; ? Sevin Lletty- 

 rhyddod. 



Bemarlis. — This shell seems to have the transverse ribs rather sharper and 

 narrower than in the type-form, and those of the opposite sides nearly or quite 

 unite on the carinated dorsum. There are three internal casts of this form 

 [28050 — 52] in the Jermyn Street Museum which have come under my notice, 

 and one from the same locality in the Sedgwick Museum, Cambridge. Another 

 specimen in the latter Museum from the Lower Llandovery of Sevin Llettyrhyddod, 

 which probably belongs to the same species, shows the distal portion of the outer 

 whorl ornamented with equidistant granulated thread-like transverse lines covering 

 the ribs and interspaces and having the same general course as the former so as 

 to meet the carina at an angle of 75°. 



This Llandovery form here regarded as a variety of G. nodosus, Salter, seems 

 more to resemble C. retrorsus, Ulrich,^ than C. ornatus, Conr., and may prove to b.e 

 specifically distinct from Salter's shell. 



5. Cyrtolites thraivensis, sp. nov. Plate V, figs. 7 — 10. 



Specific Characters. — Shell of three whorls, coiled discoidally ; whorls in 

 contact, not overlapping, rounded, subcircular in section, with weak dorsal 

 carination, rather rapidly increasing in size, without umbilical edge or lateral 

 angulation; outer whorl crossed by 15 — 20 coarse broad low rounded to 



1 Ulricli and Scofield, op. cit., p. 861, pi. Ixii, figs. 32 — 37, 



