BRACHIOPODA. 191 



The genus Orthis was thus defined by Dalman :* 



" Testa inEequivalvis, sequilatera ; valva minori subplana, majori convexa. 

 " Margo cardinalis rectilineus, latus, foramine deltoideo sub nate valvae 

 majoris." 



Nine species were cited as examples of the genus, and in the following order: 

 0. ? peden, 0. striatella, 0. zonata, 0. calladis, 0. caUigramma, 0. testudinaria, 

 0. basalts, 0. eleganiula, 0. demissa, 



Mr. Davidson quite properly takes exceptionf to the use of the first of these 

 as the type of the genus since the author himselft expressed a doubt of its 

 validity by the use of the interrogation point, and the shell proves to be a 

 strophomenoid (Strophonella).§ The second species, 0. striatella, was taken by 

 Fischer de Waldheim, in 1837|| as the type of his genus Chonetes, and with 

 entire propriety, as its generic character was also placed in doubt by Dalman 

 in his description of the species. 



Orthis zonata, the third species, was referred by de Verneuil^ to Orthisina ad- 

 scendens, Pander, but the figure of this species given by Dalman indicates that 

 it had an open delthyrium, though it is quite possible that the deltidium had 

 been destroyed in the original specimen, as frequently occurs in such fossils. 

 Little is known of this species, but under the now accepted rules of priority 

 it should be taken as the typical form of the genus. This procedure, however, 

 would be impracticable at the present time, and would create a deplorable 

 disturbance in nomenclature without giving any beneficial result. The 

 fourth species in the list, 0. calladis, and the fifth, 0. caUigramma, are well 

 known and very closely allied to each other. They are characteristic members 

 of Silurian faunas, ranging from the Llandeilo to the Wenlock formations,** 

 and represented in America by 0. tricenaria and 0. disparilis, Conrad, of the 



* Uppstallning: och Beskrifning' af de i Sverige funne Terebraluliter, loc. eit. pj). 9B, 97 ; pi i, fig-s. 5 a, 

 b, 6 a-d ; pi. ii, figs. 1 a-e, 2, 3 a-d, 4 a-e, 5 a-e, 6 a-ff, 7 a-d. 



t Introduction to British Fossil Brachiojioda, p. 103, 1853, and General Summary, p. 377. 18S4. 



I Dalman, op cit, p. 110. 



§ See Davidson, British Silurian Brachiopoda, p. 304. 1871. 



II Oi'yct. Gouvern. de Moscou, part ii, p. 134. 



If Geologic de la Russie d'Europe et des Montagnes de I'Oural, p. 203. 184.5. 

 ** British Silurian Brachiopoda, p. 245. 



