358 Prof. T. R. Jones and Dr. H. B. HoU on the 



giving a broad ovate outline to the ventral surface of the closed 

 and perfect carapace (fig. 11 c), which has the real marginal 

 rims besides. 



In some smaller specimens (xLii, said to be of " very 

 local " occurrence by Mr. Vine) the margin is narrower and 

 simple, and the front and hind lobes are confluent below. 



Taking the varieties together, the width of the free margin 

 and the ventral confluence of the lobes are variable, being 

 different in individuals. In fig. 12 (Mr. Smith's no. 22j the 

 front and middle lobes are closer together than usual, and the 

 flange has not put on the crimped or goffered pattern. 



In fig. 13 a the hypertrophy of the anterior lobe (which 

 is not very common in this species) has misshaped the valve 

 and encroached greatly on the frilled border. The reticulation 

 on the valve is irregular, but on the " big lobe " it is small, 

 neat, and elegantly regular (fig. 13 b). 



E. Boll figured and described some Beyrichice of this alli- 

 ance in the Zeitschr. d. deutsch. geol. Ges. vol. viii. 1856, 

 pp. 321 and 324, as B. Jonesii^ Boll, figs. 1 and 2 ; B. spinu- 

 losa [nodulosa, Boll, 1862), fig. 3 ; and 5. hians, Boll, fig. 4, 

 from the drifted blocks of Upper-Silurian limestone found in 

 North Germany. In 1862, ' Archiv Ver. Freunde Natur. 

 Meklenburg,' 16. Jalirg. pp. 133, 134, B. sjnnigera, Boll, 

 fig. 7, and B. Maccoyana^ Jones, fig. 9, were added from the 

 same source. 



The margin is tubercled in B. nodulosa^ and marked with 

 prickles in B. spinigera ; but in the other three the marginal 

 frill is radiately striate, with some variations in pattern and 

 intensity. The lobes differ in their proportions in all. B. 

 Mans is so called because in the described valve (unique ?) the 

 antero-ventral edge is, as it were, pressed inward and upward 

 (projecting at one spot obliquely outward),so that the carapace 

 gaped there when the valves were closed, if the notch be a 

 real feature and not the result of local accident. 



Smith's no. 13, small. Hailway-cutting, Much-Wenlock. 

 14. Railway-cutting, Coalbrook Dale. 

 17. Blue Holes, Rushal Canal, Walsall. 

 20. Railway cutting, Coalbrook Dale. 

 22. Lincoln Hill, Ironbridge. 

 25 (fig. 13 a, b), with " big lobe." Railway- 

 cutting, side of Severn, Ironbridge. 



27. Railway-cutting, side of Severn, Ironbridge. 



28. Railway-cutting, side of Severn^ Ironbridge. 

 Vine's no. XLii. J 



XLiiii. (fig. 11). >Tickwood Beds. 



LXVI. j 



