24 BRITISH DEVONIAN BRACHIOPODA. 



Spirifer Archiaci, Be Vernev.il. Geol. of Russia, vol. ii, p. 157, pi. iv, fig. 6. 18-15. 



— Murchisonianus, Be Kon. De Yern. and Keys., Geol. Russia, vol. ii, pi. iv, fig. 1 , 



1845. 



— DISJUNCTUS, Bav. Quarterly Journal of Geol. Soc, vol. ix, p. 354, pi. xv, figs. 



1—5, 1853. 



— Verneuilii, M'Coy. British Pal. Fossils, p. 3/G, 1852. 



— disjunctus, Murchison. Siluria, 2nd edition, p. 299, fig. 4, 1859. 



— Barumensis, Sow. MS. Salter, Journal Geol. Soc., vol. xix, p. 480. 



Spec. Char. Shell variable in shape, transversely semicircular or subrhomboidal ; 

 hinge-line usually as long as the width of the shell, with the cardinal angles slightly 

 rounded, or extended to a greater or smaller extent, in the shape of long, attenuated, 

 contracted prolongations ; valves convex, sometimes gibbous. In the dorsal valve the 

 mesial fold is sharply defined, of moderate convexity and elevation ; in the ventral valve 

 the sinus is concave ; beak produced and moderately incurved ; area triangular, flat, or 

 concave, and of greater or smaller dimensions ; fissure partly arched over by a pseudo- 

 deltidium in two pieces. The surface of each valve is ornamented by from forty to ninety 

 small radiating ribs, with interspaces of almost equal width. The ribs are simple on the 

 lateral portions of the shell, but increased in number to a small extent on the mesial fold 

 and sinus, by means of intercalated ribs, wdiich appear at variable distances from the beaks; 

 the whole surface is crossed by numerous, fine, contiguous, concentric lines. Dimensions 

 variable, some very large examples having attained as much as two or more inches in 

 length, by three or three and a half inches in width ; but the larger number possessed 

 smaller proportions. 



Obs. This very important Middle and Upper Devonian species has been described and 

 illustrated under many denominations ; but I quite concur with those palasontologists who 

 have considered Sp. calcarata, Sp. extensa, Sp. gigantea, Sp. inornata, Sp. Verneuilii, Sp. 

 Lonsdalei, Sp. Archiaci, and Sp. Murchisoniana, and one or two more, as mere synonyms or 

 variations in shape of a single species. Sp. protensa was founded on a single decorticated 

 and injured specimen of what I take to be a mere variation in shape of the shell under 

 description. Sp. grandava has been described from such very imperfect material that it is 

 hardly safe to offer any opinion as to its specific value, further than to say that Phillips' 

 figure looks very like a variation in shape of Sp. disjuncta, and that the author 

 himself admits that it is " decidedly allied to Sp. gigantea, but with only half the 

 number of lateral ribs." It must be borne in mind that Sp. grandava is a small 

 shell, while Sp. gigantea is a very large or fully grown condition of the species, and is 

 consequently possessed of a larger number of ribs. The term Sp. Barumensis appears to 

 be a local name given to a large variety of Sp. disjuncta, with an unusually developed area ; 

 but the area is also very large in some examples of Sp. disjuncta proper, and cannot, there- 

 fore, be made use of as a specific character. I quite coincide with the observations made 

 by Professor M'Coy, that, " when the shell approaches its adult size, it becomes the 



