BRITISH SILURIAN BRACHIOPODA. 173 



as jet only three examples of it have been discovered. The Rev. H. G. Day picked up 

 one specimen from among the dedris of the old Wenlock-limestone Quarry at Bentliall 

 Edge, and another at Dudley, and liberally placed them both in my collection for safe 

 keeping. It is remarkable that, although Mr. Maw had some eighteen tons weight of 

 Wenlock Shale, taken from different horizons and locaUties carefully washed, and had the 

 old Wenlock quarries carefully hand-picked, not another specimen of the shell could be 

 discovered. 



In Sweden it occurs at the same geological horizon, and does not appear to be so very 

 rare there. Professor Lindstrom quotes the fossil from Lansaant, Lutterhorn, Fiiro, 

 Likershamm, and Wisby (Gothland). 



Genus — Skenidium, Haii, I860 = Mptrophora^ Kayser, 1871. 



76. Skenidium (Orthis) Lewisii, Bav. Sil. Mon.,Pl. XXVT, figs. 4—9. 



At p. 208 of my ' Silurian Monograph ' I described the exterior and interior of this 

 pretty little species under the name of Orthis Lewisii, and then pointed out that it 

 differed much from its congeners by the internal characters of its dorsal valve. I 

 described and figured the elevated triangular septum with converging saucer-shaped 

 hinge-plates, and intimated that in the Devonian rocks of Perques there occurs another 

 small, similarly-characterised species, to which Mr. Bouchard had given the manuscript 

 name of Orthis Deshaysii} 



In 1860 Professor Hall proposed a new genus, Skenidium iov my so-termed Orthis 

 Lewisii and similarly-organised forms, giving as his type Skenidium insignis. Hall, an 

 American species.^ 



In his ' Beschreibung Eifel. Brachiopoden,' p. 217, 1853, Professor Schnur describes 

 as my Orthis Lewisii a much larger Devonian species, to which the name of Orthis 

 areola was subsequently given by Quenstedt in 1871 ; and in the same year Dr. Kayser 

 proposed for it and for my 0. Lewisii the generic came of Mystrophora? 



We are, therefore, at present acquainted with several closely-allied forms of the genus, 

 both in the Silurian and Devonian formations. 



Thanks to Mr. Maw's extensive washings, I have been able to examine a large number 

 of perfect specimens of my Wenlock type. It is always a small shell, and never, so far 



1 See also E. Rigaux's paper, " Description de quelques Brachiopodes du terrain devonian de Terques," 

 •Bull, de la Soc. Academique de Boulogne,' vol. i, fig. 10, 1872. 



- ' Thirteeenth Annual Report of the Eegents of the State Cabinet,' p. 70, 1860. 



3 "Die Brachiopoden des Mittel- und Ober-Devon der Eifel," 'Zeitsch. Deutsch. geol. Gesellschaft,' 

 p. 614, 1871. 



