BRITISH SILURIAN BRACIIIOPODA. 107 



In my ' Silurian Monograph ' I placed with the genus Merisfella A. tumida. Dal., 

 M. aiifjustifrons, M'Coy, M. dklyma, Dal., M. Iceviuscula, Sow., M. Circe, Bar., 31. ? 

 Madareni, Haswell, M. ? crassa, Sow., M. furcata. Sow., and M. ? subundata M'Coy ; 

 but it is very uncertain whether any of these are really referable to Prof. Hall's genus. 



We know that M. tumida is a WMfjieldia, M. didyma a Meristina, and 31. 

 Iceviuscula probably an Athyris. Unfortunately, we know as yet nothing concerning the 

 attachments of the spirals in British specimens referred to i¥. ? Circe and the others ; and 

 until their interiors shall have been properly investigated it is not possible to determine 

 the genus to which they belong. None of the British Silurian spiral-bearing species 

 developed by Mr. Glass have shown the rings of 3feristeUa, consequently we cannot at 

 present assert that the genus occurs in our English rocks, and, indeed, recent investigations 

 have proved beyond doubt that until the internal characters have been determined in any 

 spiral-bearing species it is hazardous to speak confidently on what may be the character 

 of the loop from the mere inspection of the exterior. The presence or absence of the 

 shoe-hfter process is often revealed on the exterior of the beak or posterior portion of the 

 ventral valve by the presence in 31erisfa of two deviating lines, which do not occur in 

 3ferisiella, and which may so far be of help, although they do occur in Whitfieldia. 



Genus — Whitfieldia, Dav., 1881. 



9. Whitfieldia tumida, Balm., sp. Dav. Sil. Mon., PI. XI, figs. 1 — 13 \ and Sil. Sup., 



PI. V, figs. 5, G, PI. VI, figs. 1 to 9. 



Atrypa tumida, Dalman. Vet. Akad. Handl., p. 134, pi. v, fig. 3, 1828. 



Meristella tumida, Bav. Sil. Mon., p. 109, 1866. 



Meristina Maria, J. Hall. Pal. New York, vol. vi, p. 299, 1867; 



Whitfieldia tumida, Dav. Geol. Mag., New Series, vol. viii, p. 156, April, 1881. 



The external characters of this species have been fully described at p. 109 of my 

 ' Silurian Monograph,' and I gave one figure showing the spiral appendages, and others 

 exhibiting the muscular impressions. Since then the Rev. Norman Glass has 

 been able not only to expose the spirals, but to take them entirely out of the 

 shell, or from the hard, sparry matrix with which they were surrounded, so that they can 

 be examined in every direction (see ' Sup.,' PI. VI, figs. 3, 3a, 3i^, 3c). He has also 

 completely excavated the inner side of one of the spiral cones, so that when held up 

 between the eye and the light the various convolutions can be seen as a transparency. 



