Appendix. 223 



Spirifer per/ame/losi/s, J. Hall, var. densi/ineata, iiov. 

 (PI. IV., Fig. 1, 2; PI. v.). 



Description. — Shell larfje, semicircular ; extremities obtuse to 

 acutely pointed. Ventral valve gently arcuate, beak well pro- 

 jected beyond the cardinal line ; dorsal valve strongly convex 

 towards the middle. Cardinal area moderately high. Median 

 sinus wide tuid deep ; median fold moderately wide and some- 

 what depressed or even concave on the top. On either side of 

 fold and sinus, four strong, subangulate to rounded plications, 

 and indications of two more, r.ear the cardinal line, nearly obso- 

 lete. Shell-surface with cimcentric lamellge as in the specific 

 form, but more distinct ; radial surface stride well developed, 

 closely arranged and almost continuous from beak to margins. 

 AVidth along cardinal line in a typical example, 55 mm. Length 

 from beak to anterior margin, approximately 35 mm. 



Observations. — Tte present variety, densilineaia., differs from 

 the type form in the more distantly-spaced surface lamellae of 

 the shell, and the persistent striae. Tlie type species was de- 

 scribed by J. Hall from the Lower Helderberg Group (shaly 

 limestone) of the State of NeAv York. 



In a former paper, giving a list of Silurian (Yeringian) fossils 

 from the Croydon District, I included a spirifer there referred 

 to as 6". perla/nel/osiis, var. nov., and bracketed it with McCoy's 

 S. sulcata. The smaller examples of the new variety densilhieata 

 show certain marked attinities with those figured by McCoy under 

 Hisinger's specific name, and at the time it seemed highly prob- 

 able that they made a continuous series of one variable species. 

 A further examination of a large number of Yeringian .spirifers 

 shows, however, that McCoy was right in regarding his specimens 

 from Yering as identical with Hisinger's species, the chief and 

 fairly constant differences between the two forms S. perla- 

 7nellosus, var. deusilineata, and aS'. suJratus being the higher 

 delthyrium, the closer lamellation, more numerous plications, 

 and interrupted stride of the latter. Tlie Croydon examples 

 should, therefore, be referred to Spirifer suicaius, Hisinger sp. 



1 Pal. N. York, vol. iii., 1859, p. 201, pi. xxvi., f\«s. 1, i. 

 •2 Vict. Naturalist, vol. xxiii., 1906, p. 239. 



