SPIRIFERA. 225 



surface of Sp. laminosa ; indeed, some examples of this last shell so closely resemble several 

 Derbyshire specimen of Sp. subconica as to have puzzled me extremely, and to have almost 

 made me consider both it and M'Coy's species as synonymous. Again, other examples of Sp. 

 laminosa have so narrow an area as to differ much from Martin's shell. The ribs also in 

 JSp. subconica appear relatively stronger and less numerous than in the generality of 

 specimens of Sp. cuspidata. I therefore for the present, and until the question can be 

 definitely settled by the discovery of a larger number of Derbyshire specimens of S. sub- 

 conica, prefer to retain this last (as I have done in p. 48 of the present Monograph) as a 

 distinct species. It is unfortunately very rare to find specimens of Sp. cuspidatus with the 

 shells preserved, so that we are still uncertain whether its external sculpture was similar to 

 that of Sp. subconica ? 



Spiripera glabra, Martin (p. 59). Plate XI, figs. 1 — 9 ; and Plate XII, figs. 1 — 12. 



This is an excellent but most variable species, or a type round which are clustered 

 many modifications not sufficiently marked to constitute separate species ; for although the 

 typical form of Sp. glabra possesses smooth valves, it is not uncommon to find in other 

 and exceptional examples faint indications of lateral plication, obscurely flattened, or 

 slightly rounded ribs ; the fold and sinus remaining always smooth. These modifications 

 lead us gradually to such forms as Sp. rhomboidalis, M'Coy, (p. 57, PI. XII, figs. 6, 7), 

 which are likeAvise in all probability mere modifications of Sp. glabra. 



Spirifera lineata, Martin (p. 62), Plate XIII, figs. 4 — 13; and Plate LI, fig. 15. 



When describing Sp. lineata, at p. 62, I had not seen any examples in which the shell 

 was perfectly preserved, but the subsequent discovery of several excellent specimens in 

 Scotland, as well as in India and America, has shown that externally the surface was 

 covered with numerous concentric ridges, rarely in any place more than a line apart, but 

 usually very much closer, and from each of which projected numerous, closely-packed 

 spines, which thus formed a series of spiny fringes overlaying each other all over the 

 shell. When the spines were absent, which is the general condition in which the shell 

 is found, the surface appears marked by numerous and regularly imbricated lines, the 

 radiating ones being produced by the small elevations from which each spine took its 

 rise, as I have attempted to show in the enlarged figure in PI. LI, which is very different 

 from the irregular manner in which the spines are scattered over the surface of Sp. Urii, of 

 which PI. LI, fig. 16, is an illustration. 



