﻿CALYMENE. 



95 



specimens we have seen, 1 and is also deeper in the body; the vertical height of the very 

 convex form being exactly half the width. Few specimens have the height greatly more 

 than one third. In some, fig. 16 for instance, the marginal furrow is continuous all 

 round the front. Eig. 14 has scarcely any interval behind the thick front margin and 

 the glabella. 



Var. pulchella, Dalman ; Palaeadae, p. 35, &c, has the glabella narrow in the young 

 state; our fig. 19 may very well represent such a form. The head is more triangular, 

 and the glabella narrower than usual. Fig. 11 has the same character. Fig. 16, on the 

 contrary, has a wide short glabella. But all these variations are within narrow limits. 



There are differences cf proportion in the tail. Some have the length as ten, to a 

 breadth of eleven. A second has it in the proportion of seven to ten. In others it has a 

 length of five, to a breadth of seven. And there are all intermediate proportions ; I 

 figure a variety from Mr. Allport's collection, which differs more from the ordinary 

 form of the species than any other Upper Silurian specimen I know. I call it 



Var. Allportiana ; — capite trigono,f route protluctd, glabella breviore. 



Fig. 20. 



In this variety the knots on the axis are very strong ; the 

 fulcrum is further out than usual, the glabella more sunk, and 

 the front so much produced as to suggest the idea of a strictly 

 intermediate variety between this and the preceding species. 

 Such specimens as this tend to shake our faith in species, and 

 make us ready to believe that they are after all only con- 

 firmed varieties of some more common type. Even if this be 

 true, they are not, for this reason, of less consequence either to 

 the naturalist or to the geologist : nor is it necessary to extend 

 the idea indefinitely to genera and families. 



Fig. 12 shows decided knots down the sides of the axis, 

 and this is very probably Dalman's variety tuber culata. Figs. 

 15, and in part 16, also show them; they are absent in the 

 majority of Dudley specimens. But these variations are all 



slight compared with the amount of difference seen on comparing the Dudley fossil 

 with the Lower Silurian forms distinguished under the name C. senaria. 



The internal casts figured from the Woolhope beds, PI. IX, fig. 1, and from the Llando- 

 very beds, PI. IX, fig. 2, show a tendency to a narrower and shorter form of the glabella ; 

 and some Dudley specimens also tend this way. And it will be well in comparing C. Blu- 

 menbachii with its var. brevicapitata, to bear in mind that we must compare casts with casts 

 in order to understand the amount of difference. For instance, PI. IX, fig. 1, is that of 



1 Another specimen in the Mus. P. Geology, imperfect, but as large as our central figure, has the 

 granulation remarkably close, covering the whole surface. And, whenever the true surface is preserved by 

 careful cleaning of the specimens, this character is more or less conspicuous. 



C. Blnmenbacliii, var. All- 

 portiana, from Dudley. 

 Mr. Allport's collection. 



