278 BRITISH SILURIAN BRACHIOPODA. 



Genus — Orthisina, jy Orhigmj, 1849. • 

 See "General Introduction," p. 104. 

 0. ADSCENDENS, Pander (sp.). 0. anomala, Schlotheim (sp.). 0. Verneuilii, D" Eicliwald (sp.). 



This genus seems well distinguishable from Orthis and Strophom.ena by its external 

 and internal characters. Externally it has always its fissures entirely arched over and 

 closed by a pseudo-deltidium, this last being generally, and during at least a portion of 

 the animal's existence, perforated near its extremity by a circular foramen. The 

 interior of both valves is also exceedingly remarkable, and I was able to illustrate their 

 characters in the ' Geologist ' for March, 1859, pi. iv, figs. 17 — 19, from some very perfect 

 valves of OrtJdsina anomala, presented to me by Prof. D. Schmidt, of St. Petersburgh. A 

 glance at these figures will at once convince any observer as to the necessity of retaining 

 the genus Ortldsina for the reception of these curious shells. In 1853, and for some 

 time later, from an imperfect knowledge of the true character of Ortldsina, I had, along 

 with others, most erroneously combined with it in the same genus 0. crenistria and 0. 

 pelargonatus, which have nothing to do with it, these last being representatives or 

 types of Prof. King's genus, or sub-genus, Strejjtorhgnchus. 



I am acquainted with only one British species of the genus, viz. OrtJdsina adscendens. 

 Pander, sp. ; for, as has elsewhere been shown, the so-termed OrtJdsina Scotica of M'Coy 

 does not belong to the genus, and is, in fact, nothing more than a variety of OrtJds 

 calligramma. I do not know, however, whether it would not have been more in 

 accordance with the rules of priority, had D'Orbigny, instead of proposing a new genus, 

 contented himself with Pander's generic denomination of Pronites, which had been 

 proposed in 1830, for the shell in question. 



Orthisina adscendens, Pander (sp.). PL XLIX, figs. 27 — 29. 



Pronites adscendens, P. plana, P. rotunda, P. convexa, P. alta, P. pr^ceps, 

 P. tetragona, P. lata, p. excelsa, Pander. Beit. zurGeol. des Russ. Reiches, 



pi. xvii, figs. 2 — 6, pi. xviii, figs. 1 — 5 

 (according to M. de Verneuil), 1830. 

 Orthis adscendens, Von Buck. Mem. Soc. Geol. Fr., vol. iv, p. 211, pi. ii, fig. 10, 

 1847. 



— PRONITES, Id. Beitr. ziir Geol. Russl., p. 20, 1840. 



— — B'Eich. Sil. Syst. in Esthl., p. 148, 1840. 



— ADSCENDENS, Id. Urwelt Russl., part i, p. 1.5, 1840; and 0. pronites, 



part ii, p. 145, pi. iv, fig. 1, 1842. 



