22 ORDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



Reviarks. — The original specimens of Euomplialus tenuistriatus [p. 03] and 

 E. perturhatns [6964] are in the Jermyn Street Museum. Both are in a poor state 

 of preservation, the latter being especially poor as well as distorted, so that a 

 satisfactory diagnosis of specific characters is impossible. It has generally been 

 considered that these two species are identical, and owing to the pre-occapation of 

 the name teiiulsfrvittis by a Carboniferous species of Belleroph.on, the name per- 

 tnrhatus is usually applied to this fossil. It is a common and well-marked species in 

 the Upper Arenig and especially the Llandeilo of Wales, but it is very rare to find 

 a well-preserved and uncrushed example. Salter says that it is one of the most 

 characteristic shells of the Llandeilo Flaws in North and South Wales. 



The type-specimen of E. tenuistriatus [p. 63] consists merely of the impression 

 of the exterior of an imperfect shell. The umbilicus is open and shallow. The 

 whorls rapidly increase in size and are higher than wide, with gently convex sides; 

 the dorsum seems to have been subangular and carinated ; the transverse lines are 

 equal, equidistant, and closely-placed and arch back simply but obHquely and seem 

 to meet the carina at about 30°. No slit-band can be detected. 



The type-specimen of E. pertnrhatus [6964] is an internal cast, which accounts 

 for its smooth appearance, and is much crushed and distorted. The umbilicus 

 seems to be larger and the whorls to increase more slowly in height than in E. tenui- 

 striatus, though this may be due to the distortion which the shell has suffered. 

 The type of E. pertnrhatus was obtained from the Llandeilo Flags of Pensarn, 

 Caermarttien. 



In some questionable specimens from Shelve there are 2 — 4 very fine transverse 

 lines between the stronger ones, the latter being further apart than in the type, 

 though tliey are closely crowded near the mouth. 



The true generic position of these shells is somewhat doubtful, but they are 

 most perhaps referable to Oxydisciis, agreeing in general shape, degree of enrolment 

 of the whorls, open umbilicus, and ornamentation. Salter's reference of them to the 

 genus Belleroplion is certainly incorrect, for this name, as now understood, is 

 restricted to another group of shells with completely different characters. 



Considerable doubt must still exist as to the identity of Sowerby's E. tenui- 

 striatus with E. perturhatus, the rapid enlargement of the whorls, large round 

 aperture, and angle at which the striae meet the dorsal edge, being points of 

 difference. The poor condition of the types renders an accurate diagnosis 

 impossible. 



5. Oxydiscus ? llanvirnensis (Hicks). Plate IV, figs. 9 — 11. 



1875. Bellerophon llanvirnensis, Hicks, Quart. Journ. Geol. Soc, vol. xxxi, p. 188, pi. xi, figs. 1, 2. 



Specific Characters. — Shell sublenticular, compressed, of 4 — 5 whorls, the 

 outer whorls rapidly increasing in size and height, scarcely overlapping ; dorsum 



