64 BRITISH CARBONIFEROUS BRACHIOPODA. 



several authors still maintain Sp. lineata, Sp. imhricata, and Sp. elliptica to be specifically 

 distinct ; but, after a long and attentive examination of a very numerous series of all those 

 shells, at different stages of growth and from various localities, I have discovered so many 

 intermediate shapes that it has appeared to me impossible to arrive at any other conclusion 

 but that they are all variations of a single species. This view was similarly expressed in 

 1843 by Professor L. de Koninck, but contested in 1855 by Professor M'Coy, who, 

 having enumerated the specific characters of Sp. elliptica, observes — " I agree with Mr. 

 Phillips in considering this quite a distinct species from Sj). lineata with which M. De 

 Koninck has united it. At all ages and sizes it is more transverse, more depressed, the 

 beaks are further apart, and, above all, the species is distinguished by the sinus in the 

 front margin and the strong mesial hollow extending to the apex of the beak. It is only 

 when the shell is removed that the comparatively strong radiating striae figured by Phillips 

 are seen. The reticulations exactly resemble that of Sp. lineata." 



While speaking of Sp. imhricata, the same author further observes — " This species is 

 very easily distinguished from Sp. lineata, with which some Continental authors unite it, 

 by the great width and coarseness of the concentric lamellar ridges, and the much fewer, 

 broad, obtuse, longitudinal fimbriations in a given space. It is also less wide, has generally 

 some trace of mesial hollow, and has an unusually coarse fibrous tissue under the lens." 

 And again, under Sp. lineata, he states — " This species, from the peculiar structure of the 

 surface, and the slight divergence of the dental lamellas with the strong mesial septum, was 

 originally combined in my "Synopsis' (of Carb. Foss.) with Sp. imhricata, S. reticulata, 

 S. microgemma, &c., into a little group called reticularia. There is a fine submedian 

 impressed line, apparently a fracture, visible in many specimens from the beak to the 

 front margin." 



From the statements here made it will be perceived that the most important distinctions 

 Professor M'Coy can suggest between Sp. elliptica and the other two shells are that 

 Phillips's species possesses " a sinus in the front margin and a strong mesial hollow 

 extending to the apex of the beak ;" but these distinctions lose much of their importance 

 from the fact that in some specimens of true Sp. lineata and imhricata there also exists a 

 sinus and mesial hollow extending to the apex of the beak. The beaks are likewise not 

 always approximate in the last two shells, although more commonly so than in Sp. elliptica. 

 All three are often extremely transverse, and, as admitted by Professor M'Coy, the 

 reticulations of Sp. elliptica and Sp. lineata are exactly similar. 



It will also be found that in different examples the radiating striae and concentric lines 

 or ridges vary in their degree of strength and proximity; in some (figs. 8 and 10) the 

 decussating lines are so fine and so close that the shell appears almost smooth, while at 

 other times the concentric ridges are much stronger and more separate than the radiating 

 ones, which vary both in number and proximity, and thus constituting the only appreciable 

 difference between the typical examples of Sp. lineata, figs. 4, 5, 6, 9, and Sp. imhricata, 

 figs. 11 and 12, of authors. 



