50 ORDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



Street Museum [6669] from Horeb Chapel, but the details of the ornament of the 

 slit-band and transverse lines from the specimen [28090] from Malvern. 



The description of the species B. striatus from the Upper Ludlow Tilestones 

 of Felindre which Sowerby gave is as follows: " Carinated, covered with sharp 

 striae parallel to the edge of the aperture; apex (spire?) very small, convoluted; 

 aperture cordate (with a narrow deep sinus in the front V) ; keel flattened at 

 the edge and transversely striated." McCoy described the Ludlow examples 

 from the Tilestones of Horeb Chapel, Llandovery, as follows: "Involute, sub- 

 compressed, of about one and a-half very rapidly enlarging, completely exposed 

 whorls ; section of whorls obtusely cordate, the width slightly exceeding the 

 length; sides tumid, very convex; circumference with an obtusely-defined, broad, 

 prominent flattened keel; umbilicus small; surface with fine sharp stria?, trans- 

 verse on the sides and keel ; average diameter five lines ; in proportion to 



diameter length of mouth , -— , width of umbilicus——. The greater width and 



100 100 ° 



tumidity of the sides, fewer and more rapidly expanding whorls, and consequently 



greater size of the last volution and wide obtusely flattened keel separate this 



species from //. carinatus (Sow.)." 



28 

 The specimen [<>669 ^— •] in the Jermyn Street Museum (formerly in the 



yld 



Geological Society's Museum), which is recognised as Sowerby's type, and is 

 marked "Upper Ludlow, Horeb Chapel," consists of a well-preserved internal cast 

 of a small shell measuring 12 mm. in height. It is composed of 1-| or 2 whorls. 

 The umbilicus is perforated, possibly as the result of the inner whorl beine 

 broken away. The outer whorl very rapidly increases in size, especiallyin height, 

 and is somewhat compressed, being higher than wide, with a subangular dorsum 

 and slightly raised flattened carina. The height of the outer whorl at the mouth 

 is just over three-fourths the total height of the shell, being 85 mm., and its 

 width is about 7 mm. The umbilicus is therefore far below the centre of the 

 shell. The acuteness of the carination of the dorsum decreases somewhat towards 

 the mouth, and the sides of the whorl become more swollen and convex. The 

 slight flattening of the carina probably indicates the presence of a slit-band. The 

 ornament shown on a fragment of the external impression of the shell seems to 

 consist of fine, sharp transverse striae bending back rather suddenly to meet the 

 carinal eilge at 30° — 45°. In another specimen [28090] from Malvern in the 

 Jermyn Street Museum labelled II. murchisoni, the ornamentation, which is well 

 preserved, consists of thin transverse lamellae with fimbriated edges as in T. 

 pharetni (Lindstrom), 1 hut the lamellae are closer and more regular than in that 

 species. The slit-band is well seen, and shows strongly arched, widely separated 

 lunulas, as in that species. 



1 Lindstrom, <yp. oit, p. 83, pi. vi, tigs. 39 — 51. 



