RHYNCHONELLIDtE. 



153 



appear to be as large as some of those from Sweden and the Baltic provinces, if we are to 

 consider Eichwald's Pentamerus EstJwmis ('Bull. Soc. Imp. Nat. Moscou/ part i, p. 91, 

 1854, and ' Lethaea Rossica, Periode Ancienne,' vol. i, pi. xxxiv, fig. 23, 1859) as a synonym 

 of the shell under description. I have myself seen specimens of the shell so named, sent to 

 me by Prof. F. Schmidt, of St. Petersburg, and others given to me by Dr. Lindstrom 

 from the Middle Gothland series of Carlso, KHnteberg, and Bogekhnt, without having 

 been able to detect any difference, except the larger dimensions. Both Schmidt (p. 213 

 of ' Untersuch.') and Lindstrom consider it questionable whether this shell is different 

 from P. oblongus. At p. 789 of his ' Lethsea Rossica,' d'Eichwald enters into long details 

 in the endeavour to establish his view, that P. oblongm and P. Esthonus are distinct 

 species ; but the subject will require further examination. The British, Swedish, and 

 Russian specimens of P. oblongus, as weU as the generality of the American examples, have 

 their valves moderately convex ; but some very fine casts from Springfield and Dayton, 

 Ohio, figured by Prof. Hall in pi. xxvi of vol. ii of his 'Pal. Xew York,' are exceed- 

 ingly gibbous, measuring 4^ inches in length, 3 inches 3 lines in width, by about the 

 same in depth ; and the dimensions would be somewhat larger were the shell preserved. 

 P. Esthonus also attained those dimensions both in length and width, but with a much 

 lesser depth. 



It is admitted now by most palaeontologists that P. Icevis, Sow., is the young of 

 P. oblongus ; and if it were necessary to strictly adhere to the rules of priority, James 

 Sowerby's name, published in August, 1813, would perhaps require to be adopted in 

 preference to that of oblongus, given to the adult shell by Mr. J. de C. Sowerby in 1839 ; 

 but when we read over Mr. James Sowerby's unsatisfactory description,^ and look at his 

 small, very incomplete figure, we think it preferable to preserve for the shell the now 

 generally adopted and wxU-known designation of oblongus. In 1839 Mr. J. de C. 

 Sowerby described, it is true, in the ' Silurian System,' P. lavis and P. oblongus as 

 distinct species ; but, judging from the single figured fragment of a ventral valve of P. Icevis, 



1 "Pentamerus Icevis, J. Sowerby, 'Min. Conch.,' vol. i, p. 76*, tab. xxviii, fig. 2 (right-hanJ 

 figure). August, 1813. [In our PI. XIX, fig. 2, this illustration is reproduced.] 



"Spec. Char. Smooth, triangular, front rounding, beaks incurved. Much less gibbous than either 

 of the last {P. Knightii and P. Aylesfordii), free from furrows, but having slight depressions over the 

 septa; length generally less than an inch. Not having found this in a perfect state, although I have 

 had stones including hundreds of specimens, I have been doubtful whether I ought to admit it. The 

 Rev. D. Abbot, of Bedford, in May, 1812, was so kind as to bring me pieces of rolled limestone with three 

 small dividing shells, from near Hopton Court, where he thought they appeared to be left by the swell of 

 the River Teme, and formed a bank three feet or more high. Sometimes, I think, there are two species 

 iu the stone, a smooth and a furrowed one [doubtless P. liratus'], but better chance than I have had must 

 determine this ; at the same time, one formation is distinctly characterised. The same stones contain the 

 remains of Madrepores. The specimen figured is from Buildwas, Shropshire, collected by A. Aikin, Esq. 

 In some specimens I perceive the remains of small Entrochi." Near Buildwas, Shropshire, the Wenlock 

 limestone, and also the Pentamerus or May Hill sandstone, are well developed. (J. W. S.) 



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