34 BRITISH SILURIAN BRACHIOPODA. 
L. antillarum is faintly tinged with blue-green towards the umbones ; Z. eausta is reddish- 
yellow, deeply stained with brown towards the margin ; Z. anatina exhibits a peculiar 
coppery redness, heightened in parts to a shining swarthy tone of colour; and JZ. 
hians is pale green ;' but none of the many fossil species hitherto collected throughout 
the entire sequence of sedimentary deposits, from the Lingula-flags upwards, have shown 
the smallest vestige of colour; unless, perhaps, Z. Symondsii from the Wenlock Shale. 
We are, therefore, deprived of that help, so useful among the recent forms, to aid us in 
the discrimination of our fossil shells, which must, when alive, have presented the brilliant 
green, blue, and other tints so much admired in their recent congeners. Again, how 
many of the fossil forms resemble in contour such shells as the large recent LZ. tumida, 
ZL. ovalis, and L. anatina! It is, moreover, rare to meet with the internal surface, even 
in the larger number of fossil species; and it is not often that we find specimens show- 
ing the two valves united,—a circumstance easily explained by the fact, that, when 
alive, the valves were slightly gaping at each end, and closed only along the lateral margins ; 
consequently, when dead, the valves became easily separated and scattered. Until a 
carefully elaborated general monograph of this genus shall have been prepared, much 
uncertainty and vagueness must exist with reference to a certain number of the species 
and their synonyms. 
The angle formed by the junction of the slopes of the beaks has been made use of as 
a character by some paleontologists: but after having measured the angle in numerous 
species, and specimens of the same species, I found it so variable as to preclude the 
possibility of making use of it as a distinctive character of great stability or importance ; 
and, indeed, the proportions of breadth and width, though, of course, to some extent 
available, are not usually to be relied on fully : the surface-characters are best. 
In the published catalogues some twenty-five or twenty-six species (?) of British Silurian 
Lingulz have been enumerated, but of these two or three are manuscript designations, 
appended provisionally by Mr. Salter to tablets in the Museum of the Geological 
Survey, while some others are either synonyms or species not yet sufficiently determined. 
British Species apparently well determined. 
1. Lingula Lewisii, Sow. 9. Lingula attenuata, Sow. 
2. — _ tenuigranulata, A‘Coy. 10. —_ ovata, ‘Coy. 
3. —-~ granulata, Phillips. 1]. —  Ramsayi, Salter. 
4. — _ crumena, Phillips. 12. — lata, Sow. 
5. —  Rouaulti, Salter. 13. — _ striata, Sow. 
6. — Hawkei, Rouault. 14. — _ cornea, Sow. 
7. —  Lesueuri, Rouault. 15. —  Salteri, Dav. 
8. 
— Symondsii, Salter, MS. 
1 See the beautiful figures of recent Lingula published in G. B. Sowerby’s ‘Thesaurus Conchyliorum’ 
(for 1846), and in Mr. L. Reeve’s ‘ Conchologia Iconica,’ article “ Lingula.” 
