164 SUPPLEMENT TO THE 



60. Pentamerus galeatus, Dal. sp. Dav., Sil. Mon., PI. XV, figs. 13 — 23; Sup., PI. 



IX, figs. 25, 25 a. 



This well known Upper- Silurian fossil is fully described at p. 146 of my ' Silurian 

 Monograph.' It is not an abundant species in the Llandovery Rocks ; some badly 

 preserved examples were, however, found by Mrs. R. Gray at Penkill, in Ayrshire. 



61. Pentamerus ? Shallockiensis, Dav. Sil. Sup., PI. IX, figs. 26, 26 a. 



Shell nearly circular or about as wide as long ; ventral valve convex, with a wide 

 mesial fold ; beak much incurved ; surface of valve covered with numerous radiating ribs ; 

 dorsal valve not known. 



Length and breadth 15 lines. 



Ohs. — I am very uncertain with respect to the genus to which this fossil should be 

 referred, only one specimen, a ventral valve, having been procured by Mrs. R. Gray 

 from the Middle Caradoc at Shallock Mill, Girvan. It is provisionally classed with 

 Pentamerus, as it bears resemblance to some foreign, similarly-shaped forms of the genus. 



Genus — Stricklandinia, Billings, 1859 



The characters of StricHandinia are fully described and illustrated by Mr. Billings in 

 vol. ii, p. 78, of the 'Palaeozoic Fossils, Geological Survey of Canada,' 1874. He says 

 there that, whilst studying the species in the Canadian Collection, he observed that nearly 

 all those with short plates in the dorsal valve differed in general from those with long 

 plates ; he therefore proposed a new genus for their reception, and stated that the main 

 differences between Pentamerus and StricMa?idinia consisted in the internal structure of 

 the valves discovered by Mr. Salter, and in the general form first pointed out by himself. 



Stricklandinia abounds in some of the Canadian rocks, and attains there to con- 

 siderable dimensions, StricHandinia Gaspensis, Bill., measuring 4 inches in length by 

 3 in width ; of this a figure is given by Mr. Billings at p. 83 of the Canadian work 

 above referred to. Mr. Billings states likewise that neither Stricldandinia lirata nor St. 

 lens have been hitherto discovered in Canada. 



