150 ^Ir. F. Chapman on some 



by the middle lobe ; posterior angle full and evenly rounded, 

 anterior rounded and narrowed off. JMiddle of valve with a 

 short, low, transverse, clavate ridge or swelling, which pro- 

 jects a little beyond the dorsal margin. Towards the ends 

 of the valves the sides are swollen, especially near the poste- 

 rior extremity, and represent incipient lobes. Surface of 

 valves delicately pitted. Edge view of carapace elongate- 

 oval, with rounded ends. Length '44 millim.; height '266 

 milHm. 



This species is nearly allied to Beijrichia {? KIcedenia) 

 plagosa, Jones *, which was obtained from strata of Wcnlock 

 age at Beechey Island, Canada. It differs, however, in the 

 position and shape of the central lobo, which in our specimen 

 is more pronounced and projects beyond the margin ; and, 

 further, the surface ornamentation in K. gotlandica is an even 

 and delicate pitting. 



BOLLIA, Jones & Holl [1886]. 



Bollia auricularisy Jones. 



Bollia auricularis, Jones, 1887, Ann. & Mag. Nat. Hist. ser. 5, vol. xix. 

 p. 408, pi. xiii. figs. 10 a-c. 



This species is not uncommon in the Gotland washings, 

 and the measurements of the valves agree very closely with 

 those of the originally described specimens from Iroubridge, 

 Severn. 



Silurian ; Mulde, Gotland. 



Beyrichia, M'Coy [1846]. 



Beyrichia concinna, Jones & Holl. 



Beyrichia concmna, Jones & Holl, 1886, Ann. & Mag. Nat. Hist. ser. 6, 

 vol. xvii. p. 356, pi. xii. tigs. 22 a, b. 



The Gotland specimens measure about one third more than 

 the specimen figured by Jones and Holl from the Silurian of 

 Dormington, but otherwise they possess the same charac- 

 teristics. 



Silurian; Mulde, Gotland. Common. 



Beyrichia muldensis, sp. n. (PI. III. fig. 10.) 



Valve oblong, ventral margin slightly convex, ends nearly 

 equally rounded, and with a marginal raised rim round the 

 ends and the elliptically curved ventral border. Surface of 



* Ann. & Mag. Nat. Hist. ser. 3, vol. i. 1858, p. 243, pi. ix. fig. 2. 



