BRACHIOPODA. 
191 
The genus Orthis was thus defined by Dalman :* * * § ** 
“ Testa inaequivalvis, 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, O. calligramma, 0. testudinaria, 
0. basalts, 0. elegantula, O. demissa. 
Mr. Davidson quite properly takes exceptionf to the use of the first of these 
as the type of the genus since the author himself^: 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, O. 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 VerneuilH 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 . calligramma, 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 O. tricenaria and 0. disparilis, Conrad, of the 
* Uppstallning och Beskrifning af de i Sverige funne Terebratuliter, loc. dt. pp. 96, 97; pi. i, figs. 5 a, 
b, 6 a-d; pi. ii, figs. 1 a-e, 2, 3 a-d, 4 a-e, 5 a-e, 6 a-g, 7 a-d. 
t Introduction to British Fossil Brachiopoda, p. 103, 1853, and General Summary, p. 377. 1884. 
I Dalman, op cit, p. 110. 
§ See Davidson, British Silurian Brachiopoda, p. 304. 1871. 
|| Oryct. Gouvern. de Moscou, part ii, p. 134. 
Geologie de la Russie d’Europe et des Montagnes de l’Oural, p. 203. 1845. 
** British' Silurian Brachiopoda, p. 245. 
