BRACHIOPODA. 
251 
applied (type, Triplesia lateralis^ Whitfield, of the Calciferous fauna). Some of 
these early species were described as Stricklandinia by Billings {S. Arachm 
and )S. Arethusa, from the Quebec group), but the author subsequently expressed 
his conviction that they represented a distinct type of generic structure. (Pal¬ 
eozoic Fossils, vol. ii, pt. i, p. 89.) 
Some writers have assumed as the typical representative of Billings’ genus 
the species Atrypa or Pentamerus lens, Sowerby, an elongate shell of considerable 
size, from the Llandovery faunas, and allied in form and the general smooth¬ 
ness, or faint ribbing of its exterior, to the American species S. Davidsoni, 
Billings. Though the English species is mentioned frequently in the original 
discussion of the genus, we may feel more secure in the interpretation of the 
author’s intentions by assuming as the type, the form first described by him, 
S. Gaspensis, a very large and strongly plicated shell with all the characteristic 
features positively developed. 
On the brachial valve of this genus the short dental plates, at their inner 
angles, bear long crural processes. Though the expanded portions of these 
dental plates do not unite as in Amphigenia to form a hinge-plate, yet the 
development of the crura and the abbreviation of the median septa suggest 
analogy with the latter genus rather than with Pentamerus, Conchidium, etc. 
Stricklandinia is represented in the American Palmozoic by the following spe¬ 
cies : S. Gaspensis, S. brevis, S. Anticostiensis, S. Davidsoni, S. Salieri and >8. Melissa, 
all described by Billings, from the middle Silurian faunas of Canada; the last 
of these being a smooth shell, probably the same as that described from the 
Niagara dolomites of Illinois, under the name S. deformis, by Meek and Wor- 
then.* Besides these are S. Canadensis, Billings, from the Clinton group of 
the Province of Ontario, S. castellana, White, and S. multilirata, Whitfield, from 
the Niagara dolomites of Iowa and Wisconsin. 
* Geological Survey of Illinois, vol. vi, p. 502. 
