390 CARBONIFEROUS LAMELLIBRANCHIATA. 



necessary in such a large shell, entirely destitute of any locking apparatus in the 

 long posterior hinge-line, in order to keep the valves in contact. 



There can be little doubt of the propriety of placing the Sanguinolaria 

 transversa of Portlock as a synonym of 8. plicatus. The type specimen (" No. 5 " 

 of Portlock), PI. XLV, fig. 1, is now in the Museum of the Geological Survey, 

 Jermyn Street, and represents a cast of the right valve of a half-grown 

 shell. There is no diagonal ridge as shown in the original figure. Portlock 

 compares Sanguinolaria transversa (op. cit., p. 434) with 8. plicatus, and says, 

 " This is as much depressed as 8. plicata, and resembles it in form, but the 

 undulations or folds become little more distinct than the ordinary lines of 

 growth." He apparently did not recognise the fact that the type specimen of 

 8. plicata had its shell preserved, while that of 8. transversa was only a cast of 

 the interior. Another of Portlock's specimens is preserved in the same collection, 

 " No. 7 " of that author, from shale. This specimen certainly does show that 

 the sulci and rug^ were less well marked, a fact probably accounted for by the 

 muddy waters in which the shell lived (PI. XLIV, fig. 12). 



The figure of 8ohn signifer, Eichwald (oj). cit.), is probably characteristic of 

 the full-grown shell of 8anguinolites plicatus, and must be also placed as one 

 of its synonyms. The shell was obtained from the Carboniferous Limestone of 

 Sloboda, in the Russian government of Toula. 



I consider the Sanguinolaria undataoi Portlock to be a specimen of 8. plicatus 

 with the external markings very highly accentuated. The two shells seem to be 

 always found together, and no other character except the degree of accentuation 

 of the external ornament can be cited to distinguish them. Portlock {op. cit., 

 p. 598) says, "Amongst some valuable Berwick fossils, obligingly sent me by 

 the Rev. Mr. Jenkinson of Lowick, I find both the species Sanguinolaria undata 

 and 8. transversa. The specimens are perfect, and show that S. umlata was 

 nearly identical in form with S. transversa, but distinguished by the angular folds 

 of the posterior portion of the shell." M'Coy says {op. cit., p. 50-5), " This shell 

 {8. iridinoides) is distinguished from the 8. undata (Portlock) by that species 

 having numerous strong prominent ridges continued without any visible increase 

 in number or diminution in size across the body of the shell ; the anterior side is 

 also much narrower and rounded." As a matter of fact the external markings 

 vary slightly in individual specimens, and a long series of examples shows all 

 degrees of variety in markings between the extremes. I therefore place 

 Sanguinolaria undata, Portlock, as a synonym of Sanguinolites plicatus. It is 

 carious, therefore, that Portlock has described the youug, adult, and another 

 form of the same shell as three distinct species, all of which have been adopted 

 by M'Coy, who also redescribed the adult form under another name. 



This species is very common indeed in the Redesdale Ironstone series, but 



