276 
SUPPLEMENT TO THE BRITISH 
Yonng has noticed that, in addition to the concentric ridges common to the species, there 
existed narrow, widely interspaced, fine radiating lines, but this character is chiefly 
observable in the variety reticulata of Sowerby. 
14. Spirifera. trigonalis, Martin. Dav,, Garb. Mon., p. 233, Sup., PI. XXXIV, 
figs. 3, 3, 4. 
I have nothing to alter to what I said at p. 333 of my Monograph, with respect to 
this very remarkable and exceedingly variable species, and am still of opinion that Sp. 
hisulcata, Sp. grandicosta, Sp. crassa, Sp. transiens, and perhaps also 8p. triangularis, 
are extreme variations in shape or, at the very utmost, varieties of a single species. On 
examination I now find that the shell sculpture of Sp. triangularis agrees with that of 
Sp. trigonalis, of which an illustration will be found in PL L, fig. 9 a.^ In all, 
and especially so in the varieties trigonalis, bisulcata, and triangularis, the mesial fold is in 
character essentially the same, but in some examples of both trigonalis and triangularis 
it is remarkably produced, as will be seen in the figure I have added to this Supplement 
(PI. XXXIV, fig. 3). This very fine example is from Arden, near Thornliebank, 
Scotland, and collection of Mr. J. Young. I have in the same plate given likewise 
illustrations of two very fine examples of the variety bisulcata from our Scottish 
rocks (PI. XXXIV, figs. 3, 4). The greater or lesser extension of the wing-shape expan- 
sions, or of the mesial fold, will not, in the case of trigonalis, serve as a permanent dis- 
tinguishing character between it and its varieties, and the more we proceed with the 
careful examination of many so-termed species, with the help of abundant material and 
well-preserved specimens, we shall find variations in shape to be so numerous that what 
at one time we might have considered good distinguishing characters are in reality so 
regarded from imperfect knowledge and insufficient examination. I would likewise refer 
the reader to a paper by Mr.. John Young, entitled " Notes on the Occurrence and Dis- 
tribution of Sjnrifera trigonalis, and its varieties in the Coal-fields of the West of 
Scotland," 'Proceedings of the Natural History Society of Glasgow,' 1875," and from 
which I will quote a few passages. 
1 Mr. John Young, of tlie Ilunterian Museum, Glasgow, wrote me : " 1 have looked carefully at the 
best preserved exterior surface of Sp. trigonalis or bisulcata that I have in my collection, and can find no 
trace of pores at the base of the minute spines that fringe the lines of growth. The spines leave only a 
very faint impression on the surface of the shell, and do not appear to pass into the substance by any 
tubular process like that of Sp. lineata. The spines on Sp. trigonalis appear to be only little delicate 
extensions of the outermost layer of the shell. They are very much of the same nature as the spines that 
fringe the shell of Athyris Royssii, but are much smaller. Neither of these forms appearing to have tubular 
spines, I have also examined a number of species of this Spirifer to see if I could detect any minute 
perforations in its shell-structure, but I have failed as yet in detecting any trace of such." 
2 " I now call your attention shortly to a group of SpirifercB found in the Marine Limestone strata 
belonging to the well-known and common species Sp. trigonalis, Martin, and the variety bisulcata, Phil. 
