The Rev. Norman Glass — On Athyris Iceviuscula. 495 



VI. — On Athtbis ljeviuscula, Sow., sp., with the Full Dis- 

 closure OF ITS Loop, etc. 

 By the Eev. Norman Glass. 



DAVIDSON thus describes the external characters of this species 

 in his Sil. Suppl. pp. 101, 102. The description is practi- 

 callythe same as that which he previously gave in his Sil. Mon. 

 " Marginally of a somewhat elongated, pentagonal shape, truncated, 

 and slightly indented in front, broadest about the middle. Tapering 

 posteriorly. Valves almost equally convex, with a slight median 

 depression near the front in the ventral valve. Beak strongly 

 incurved, and truncated by a minute oval foramen; surface smooth, 

 marked by a few concentric lines of growth. Length 6, breadth 5 

 lines, but the generality of specimens are much smaller." Davidson 

 refers to the spirals of this species both in his Sih Mon. and in his 

 Sil. Suppl. Sil. Mon. p. 115 : "I had noticed the presence of spirals 

 in 1847, and recorded the observation in the 'Bulletin Soc. Geol. 

 France,' and Lindstrom has also detected them in a Gothland 

 specimen." In pi. x. fig. 31 of his Sil. Mon. Davidson represents 

 the dorsal aspect of the spirals, with the bases of the spirals facing 

 each other in the centre of the shell. The spirals of this species 

 are more fully referred to in Davidson, Sil. Suppl. p. 102 : " The small 

 dimensions attained by this species caused the Rev. Norman Glass 

 much trouble in his patient endeavours to work out its interior 

 arrangements. A great number of English specimens were operated 

 upon, as well as a number of Swedish ones kindly contributed by 

 Prof. Lindstrom of Stockholm. Mr. Glass has shown in a very 

 plain manner the accessory lamellae, also the hook-shaped attach- 

 ments to the hinge-plate ; but, on account of the smallness of the 

 specimens, it was not possible to expose the loop or its attachments 

 to the primary lamellee in the same manner as he had so successfully 

 achieved in Athyris piano -sulcata. We are both convinced that 

 Sowerby's species is an Athyris. In a specimen one line and a half 

 in length cleared out by Mr. Glass, there were only three coils in 

 each spiral. In another four lines in length, four coils ; and none 

 of the largest specimens have shown more than six or seven in each 

 spiral." In his Sil. Suppl. pi. iv. figs. 25, 26, Davidson gives repre- 

 sentations of the doi'sal and ventral aspects of the spirals — the 

 ventral aspect including the hook-shaped attachments of the primary 

 lamellee to the hinge-plate and the accessory lamellge of the loop. 



Davidson in the above quotation credits me with a stronger im- 

 pression than I possessed as to this species being an Athyris. 

 Certainly so far as the hook-shaped attachments of the primary 

 lamellae to the hinge-plate were concerned, and the ventral aspect 

 of the accessory lamellae, there was nothing to distinguish this 

 species from Athyris, but in Athyris the accessory lamellae are con- 

 tinued over the posterior border and about half-way down the dorsal 

 side of the spirals, and no evidence of this had been discovered 

 when the Sil. Suppl. was published — indeed those preparations which 

 I had sent to Davidson showing the dorsal aspect of the spirals 



