10 ORDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



with large, prominent, subangular apertural lobes projecting far forwards ; npper 

 lip with deep, U-shaped dorsal sinus. Interior of shell with two principal strong 

 rounded transverse thickenings, both well developed on dorsum, but dying out 

 nearly completely on sides of whorl, one snbmarginal and the other a little 

 distance behind it, both concentric to margins of apertural lobes. External 

 surface of shell with fine transverse stritB strongly arched back to form sinus on 

 dorsum [and crossed by very delicate revolving lines most distinct on apertural 

 lobes, producing minute cancellation]. 



Dimensions. — Height of shell, about 30 mm.; thickness at umbilicus, about 11 mm. 



Horizon. — Bala Series. 



Locality. — Tyrone. 



Remarks. — The shape of the apertural lobes is like that in ;S^. snhrectangularis ; 

 but the two strong internal transverse thickened bands on the dorsum having their 

 course concentric to the angulated apertural lobes, and gradually disappearing on 

 the sides of the whorl, as well as the external ornament, distinguish this species. 

 For in 8. suhredangularis there is only one transverse thickening, and it is not 

 concentric with the margin, and it is strongest on the sides of the whorl instead 

 of on the dorsum. The supposed types of S. elongatus [27991 and 27990] which 

 are in the Jermyn Street Museum, are distorted. Another fragment [28031] in 

 the same museum shows the external ornament well as in 8. crypticus. Some 

 doubtful examples occur in the Starfish Bed, Girvan. 



7. Sinuites maccallumi, sp. nov. Plate II, figs. 1 — 4, ? 5. 



8peclfic Characters. — Shell somewhat compressed laterally, with back more or 

 less narrowly rounded and whorls higher than wide. Umbilicus minute or closed, 

 situated at about two-fifths, or less than half the height of shell. Outer 

 whorl completely enveloping inner whoi'ls, higher than wide, increasing more 

 rapidly in height than width, with semi-oval cross-section. Mouth not expanded 

 laterally, semi-oval in shape, higher than wide, with deep U-shaped sinus in 

 outer lip more than one-third width of back and with bluntly pointed, obtuse, 

 subangular, apertural lobes projecting sharply forwards with inner and outer 

 edges inclined at 90° — 130°. Surface of shell with very fine transverse growth- 

 striae concentric with apertural margin. Interior with two successive low-rounded 

 transverse U-shaped marginal thickenings concentric with sinus (but suddenly 

 ending laterally), and placed close together, corresponding with constrictions 

 (represented by shallow rounded broad grooves) on surface of shell. 



Dimensions. — Height of shell, 14*0 mm. ; height of outer whorl above umbilicus, 

 9*0 mm. ; width of outer whorl above uml)ilicus, 8-75 mm. ; width of outer whorl 

 below umbilicus, 6'0 mm. 



