86 ORDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



Genus CARINAROPSIS, Hall. 



Generic Characters. — Shell composed of little more than two whorls, the inner 

 one very small, scarcely embraced by the outer, and more or less free ; outer whorl 

 very large, rapidly expanded; dorsum sharply carinated, becoming less angular 

 towards aperture; [slit-band occasionally distinguishable?]. Mouth very large, 

 with everted margins; dorsal lip thin, sinuate and centrally notched; inner lip 

 entire, reflexed [with broad thick inner plate bearing median ridge] ; inner 

 aperture to whorls covered [always ?] by triangular flat operculum. 



Ulrich and Scofield l believe that this genus should include the genus 

 Pterotheca, Salter, the Girvan representatives of which have been described by the 

 present author 2 amongst the Pteropoda. Perner, 3 however, puts Carinaropsis 

 (which he spells Carivariopsis) in his group Bucanioidea. In Zittel-Eastman's 

 'Text-book of Palaeontology' (2nd edit,, 1913, p. 523) the genus is put in a 

 family by itself after the family Bellerophontida?, but Pterotheca is included with 

 the Pteropoda and placed in the family Hyolithida?. A discussion of the charac- 

 ters of Carinaropsis and of the diverse usage of the name by various authors is 

 given by Perner. Our British specimens do not help to clear up the difficulties 

 connected with it, I have not seen any trace of a slit-band in any examples, and 

 I much doubt if forms possessing this structure should be included in this genus, of 

 which the type-species is G. carinata, Hall,* of the Trenton Group. 



1. Carinaropsis gracilis* sp. nov. Plate XIII, figs. 8, 9. 



Specific Characters. — Shell of 1 — 1^ whorls, scarcely embracing, acutely earinate, 

 triangular in section ; umbilicus small, situated at about one-fourth the height of 

 shell. Outer whorl very rapidly increasing in size to about three or four times the 

 height and width at peristome. Mouth large, much expanded laterally, trans- 

 versely elliptical in shape, with broad acute shallow V-shaped sinus in outer lip ; 

 apertural lobes rounded, very large, laterally extended and flattened, inner lip 

 somewhat deflected. Surface of shell with tine transverse stria? and growth-lines 

 concentric to margin near peristome. 



Dimension* : 



i ii 



Height of shell c. 16'5 mm. . 21 mm. 



AVidth of mouth c. 18*5 „ . 27 „ 



Horizon. — Balclatchie Group, Lower Ordovician. 

 Localities. — Ardmillan ; Balclatchie; Dow Hill, Girvan. 



1 Ulrich and Scofield, op. cit., pp. 857, 926. 



2 Reed, 'Trans. Roy. Soc. Edinburgh,' vol. xlvii, pt. ii, no. 9 (1909), p. 215. 



3 Perner, op. cit., p. 90. 



+ Hall, ' Palseout, New York,' vol. i (1847), p. 183, pi. xl, figs. 1 a— c. 



