ORTHID A. 243 
of O. calligramma the small incurved beak appears slightly above the highest point of the 
area, as may be seen in fig. 7 a, pl. xiii, of the ‘Geol. of Russia;’ but in fig. 7e of the 
same plate the small incurved beak is no longer visible. This is also observable in many 
of our British specimens from the Caradoc of Moelydd, near Oswestry, and where the 
shell most resembling the Russian type is found. M. de Verneuil informs us that 
O. orthambonites is a variety of O. calligramma which exists only in Russia, unless we. 
unite to it certain individuals of the Swedish O. callactis, Dalman. I am still uncer- 
tain, however, whether Dalman’s O. callactis is more than a variety of the shell under 
description, although M‘Coy describes it at p. 214 of his work on British Paleozoic Fossils 
as a distinct species. We may assert that the O. callactis of the ‘Silurian System’ 
is no more than a variety of O.calligramma. The fine longitudinal strive which cover the 
surface of the interspaces between the ribs, as well as the fine concentric equidistant 
lines observable on well-preserved specimens, are rarely seen on any of our Lower Silurian 
specimens, on account of their indifferent state of preservation; but they have been 
noticed both by De Verneuil, D’Eichwald, and myself, on Russian Lower Silurian 
specimens, and are well exposed in some of our Upper Silurian examples of the variety 
Davidson. Thus, while describing the var. orthambonites, M. de Verneuil writes— 
“Dans cette variété, les sillons ne sont pas finement striés dans le sens de la longueur, 
mais ils sont, ainsi que les plis eux-mémes, recouverts de fines stries transverses. Cette 
différence, souvent trés difficile & apercevoir, est la seule que nous ayons pu observer entre 
les O. calligramma et orthambonites, et encore est-il permi de croire quelle est plus 
apparente que réelle, et dépend des divers degrés de conservation de la coquille: en effet, 
presque tous nos échantillons paraissent plus ou moins altérés, la plupart ont les plis 
tout-a-fait lisses, les uns prennent graduellement des stries longitudinales, d’autres des 
stries transverses, et enfin un échantillon plus complet nous a offert quelques stries longi- 
tudinales recouvertes et presque cachées par des stries transverses. Ces différences ont 
échappé a M. Pander, dont les espéces ne sont établies que sur des rapports de longueur 
et de largeur, sur le nombre des plis ou sur les dimensions de l’area, qui sont ce quil v a 
de plus variable. Elles ont au contraire été observées par M. Hichwald, qui a appelé 
O. orthambonites \a variété a& stries transverses, et O. callactis celle a stries longitudinales. 
Nous avons préféré adopter pour cette derniére le nom O. calligramma, en nous fondant sur 
les caractéres que lui a reconnus M. Hisinger.”’ 
I know but little of the var. virgata (P]. XXXV, figs. 28, 24, and Pl. XXXVII, 
fig. 2). Mr. Salter states—<We have but one valve of this species, and Mr. 
Sowerby only figured the same valve in the ‘Silurian System.’ It agrees in shape 
pretty well with O. plana, or O. lata, Pander, having the hinge-lme somewhat shorter 
than the width of the shell. But it is of larger form, and has numerous, thirty-six or 
more, ribs, very regular and equal in size.” It occurs in the Caradoc, at Cwm-gwynen- 
uchaf, Montgomeryshire. Mr. Salter considers M‘Coy’s O. simplex (see Pl. XXXII, figs. 
10, 11) to be also a variety of O. calligramma; but this, I think, can hardly be the case, 
