238 MB. P. IAKE ON THE BRITISH [May 1 896, 



Geology, Jermyn Street, from the Upper Llandovery of Pen-y-llan, 

 seems to belong to this species. 



Affinities. — This species closely resembles A. deflexa, from which, 

 however, it may be distinguished by the following characters : — 

 (1) the external border of the genal spine in A. coronata forms a 

 curve nearly continuous with the external margin of the cheek ; in 

 A. dcflexa there is a distinct angle between the two ; (2) the tail of 

 A. coronata bears eight short points, all of which are parallel to the 

 axis, while the tail of A. deflexa bears only four spines and a rudi- 

 mentary point at each of the anterior angles. 



Synonymy. — A. coronata has been one of the most unfortunate 

 species of an unfortunate genus. At the present day it bears three 

 distinct names, all of which are in common use. It is known as 

 A. coronata in England, A. MarTclini in Sweden, and A. mutica in 

 Germany ; and even yet it is not clear which of these names it 

 ought to bear. Murchison's term quadrirnucronatus is older than 

 any of them ; but it is so entirely misleading, and his description is 

 so incorrect, that although his figure is just recognizable, the name 

 can scarcely stand. Moreover, it is possible that all palaeontologists 

 may not consider Murchison's figure unmistakable. 



The oldest of the other three names is mutica ; but although our 

 species is identical with A. mutica as figured and described by 

 Wigand, it is by no means certain that it is the same as Odonto- 

 pleura mutica of Emmrich and Beyrich. Emmrich's description is too 

 brief to be of any value ; but Beyrich's account of the species states 

 that the thorax has only 9 segments, while in his figure the spines 

 of the tail are radiate instead of parallel. Until, therefore, 

 Emmrich's or Beyrich's type has been re-examined, it is impossible 

 to apply the name to the English form. 



In 1848 Salter figured and described Acidaspis Brighfii, Murch., 

 but unfortunately, along with a specimen of the true A. BrigJiti, he 

 figured also a head and a tail of our present species. In 1853 he 

 had discovered his mistake, and proposed the name coronatus for the 

 new form, pointing out at the same time which of his figures 

 belonged to it ; but it was not till 1857 that he published a 

 description. 



In the meantime Angelin had described and figured the thorax 

 and tail of the same trilobite as A. Marklini, a name which has not 

 unnaturally been accepted in Sweden. Under the impression that 

 it belonged to a distinct species, he gave to the head of this form 

 the name of A. multicuspis. Angelin's figures are not good, but 

 Lindstrom has since given an accurate description of the species with 

 good figures ; and from an examination of the original specimens in 

 the Riksmuseum at Stockholm I am able to state that the Swedish 

 and English species are identical. 



Thus there is plenty of room for difference of opinion, and it is 

 not without hesitation that I have adopted Salter's name. But, 

 putting aside Murchison's term, Salter's was the first which was 

 applied to a recognizable figure of the species. 



