BRACHIOPODA. 251 



applied (type, Triplesia lateralis, Whitfield, of the Calciferous fauna). Some of 

 these early species were described as Stricklandinia by Billings {S. Arachne 

 and (S. Arethusa, from the Quebec group), but the author subsequently expressed 

 his conviction that they represented a distinct type of generic structure. (Pal- 

 aeozoic Fossils, vol. ii, pt. i, p. 89.) 



Some writers have assumed as the typical representative of Billings' genus 

 the species Alrypa 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 Palaeozoic by the following spe- 

 cies : S. Gaspensis, S. brevis, S. Anticostiensis, S. Davidsoni, S. Salteri and S. 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. muUilirata, Whitfield, from 

 the Niagara dolomites of Iowa and Wisconsin. 



* Geolojiical Survey of Illinois, vol. vi, p. 502. 



