554 PROF. T. R. JONES ON SOME DEVONIAN AND 



lobes are of nearly equal bulk, and unite with a broad curved junc- 

 tion below ; the middle lobe is of an irregular and reversed club- 

 shape, constricted at its upper third ; there is also a curved, low, 

 subsidiary ridge at one end, just within the margin. Abundant. 



§ IV. From Brittany^ France. 



Beyrichia, M'Coy. (See also pages 236-238, 246.) 



36. Beyrichia Guillieri, Tromelin. (PI. XXI. figs. 2a,2h, 2c.) 



Beyrichia Guillieri, Tromelin, Association Francaise pour I'avance- 

 ment des Sciences ; Compte rendu de la 4^^ Session, Xantes, 1875 

 (8vo, Paris 1876), p. 623, footnote (not figured). 



Length 2 mm. ; height 1 mm, ; thickness "5 mm. 



This is a three-lobed Beyrichia, as shown by the cast of left valve 

 in light-coloured mudstone, apparently not distorted by pressure. 

 In outline it is subovate, but straight on one edge (dorsal). The 

 two smaller lobes are club-shaped, high and rather narrow, forming 

 a fork, which opens upwards and forwards ; the front lobe is low 

 down, near the antero-ventral margin, and gently curved ; the 

 middle lobe is straight, oblique, and prominent, reaching the dorsal 

 margin. The junction of these two lobes below is continued to 

 the curved base of the large and rounded posterior or gigot lobe. 



In some respects, as for instance in the proportions of the lobes, 

 one variety of Kiesow's Beyrichia Linclstroemi^ from the Upper 

 Silurian of Gothland, namely fig. 4. pi. i. p. 5, ' Zeitsch. d. D. geol. 

 Ges.' 1888, bears a resemblance to B. Guillieri, but in other respects 

 it differs. 



The figured specimen is from the Lower Silurian (Ordovician) 

 strata at Domfront (Dep. Orne), and was kindly given by M. P. 

 Lebesconte, of Hennes. There were several individuals together. 



In the same collection (M. Lebesconte's) are numerous specimens 

 of the same species, but variously squeezed, and in some instances 

 much distorted, in the " Schiste ardoisier inferieur" (Ordovician), 

 below the " Gres de May," at Laille (Dep. Ille-et-Yilaine). One 

 specimen, somewhat shortened diagonally, from the postero-ventral 

 to the antero-dorsal region, has the two smaller lobes more vertical, 

 and all the lobes more equally separated, than in the figured 

 (normal) form ; but its thick, rounded posterior lobe is still character- 

 istic. In another case, pressure, transverse and nearly perpendi- 

 cular to the long diameter of the valve, has elongated the valve, 

 making its height scarcely a fourth of its length, and disturbing the 

 positions and proportions of the lobes. 



This was compared with some Bohemian and other species by M. 

 Gaston le Goarant de Tromelin in a footnote to a memoir by him- 

 self and M. Paul Lebesconte on the Silurian Fossils of the Depart- 

 ments of Maine-et-Loire, Loire-Inferieure, and Morbihan (Anjou 

 and South Brittany), in the Eeport of the French Association for 

 1875, referred to above. It is mentioned also in that paper at 

 p. 620, as having been first found at Domfront (Orne), and as one 



