﻿RHYNCHONELLA. 



95 



Length 25, width 26, depth 19 lines. 

 ,, 15, ,, 17, ,, 22 ,, 

 ,, 19, 20, ,, 11 ,, 



» 15, ,, 19, ,, 7?j j> 



Obs. At page 222 of his ' Geology of Yorkshire,' Professor Phillips has stated that 

 the varieties of T. acuminata are almost innumerable, and that a specific character was at 

 that time impossible. If, therefore, such was the case in 1836, I do not believe that 

 matters have materially improved since that period. It is at all times most difficult, nay 

 impossible, to convey in a diagnosis a sufficiently accurate description of a species, and 

 especially of so variable a one as that now before us ; and as figures always convey a more 

 accurate idea of any object than words alone are able to express, I have represented in 

 Plates XX and XXI all the principal and more important variations, both of specimen and 

 age, assumed by this species, and which have been selected with great care from among 

 some hundred specimens I was able to assemble from various collections and localities. 

 Every intermediate link can be found connecting such extreme cases as those, PI. XX, fig. 1, 

 and PL XXI, fig. 11, and the want of space alone has prevented their being all here repre- 

 sented. The first notice I find of this remarkable shell consists of two very good figures 

 of the typical variety, published by Andreae, in his ' Lettres ecrites de la Suisse,' pi. xiv, 

 1763, and which illustrations very closely agree with those published by Martin forty-four 

 years later. Several authors have referred fig. 1 of pi. ccxlvi, of the £ Encyclopedic 

 Methodique,' published by Bruguiere, in 1788, to T. acuminata, and it may have been 

 drawn from an example of the species, but it bears also much resemblance to some 

 specimens of De Verneuil and Keyserling's Bh. Meyendorfii, and is not so good or so 

 characteristic a representation as that by Andreae, above mentioned. It was, however, 

 only in 1809 that the shell received a specific denomination, and that of acuminata was 

 bestowed upon it by Martin, 1 who gave us at the same time a good description and 

 correct figure of two of its varieties, and which agree also very closely with those I have 

 represented in PL XX, fig. 2, and in PL XXI, fig 1. These will require to be looked 

 upon as the typical shape of the species. 



In 1822 James Sowerby describes and figures the same form, and in 1825 he repre- 

 sented two other of its varieties, which he designated by the names sulcata and plicata, 

 and to a third he applied the specific denomination of platyloba. In 1836 Professor 



1 Martin describes his species in the following words : 



" Conchyliolithus anomites {acuminatus) cordiformis lsevis, sinu margine lougissimo cuneato, s. p. 



" A petrified shell ; the original an Anomia. Perforate ; both valves convex, cordiform or heart-shaped, 

 and smooth, the surface being destitute of striae, furrows, or tubercles (the larger specimens, under a 

 glass, appear to be marked with very minute, close, and equal striae). The hinge curved, and close. 

 Foramen very minute, under the apex of the beak, which is small, sharp-pointed, and incumbent. The 

 larger or beaked valve hollowed at the back into a single wave, ending in a very long, sharp-pointed, 

 cuneiform, or wedge-shaped sinus at the margin. This very curious Anomite is not uncommon near Bake- 

 icell and Buxton, in the limestone strata ; it varies considerably in size." 



