

136 



INTRODUCTION. 



he changes the name to Aulonotreta, and objects to Professor Eichwald's denomination 

 because the shell under consideration does not resemble the old Greek coin Oholiis, and 

 does not think far-fetched names befitting ; but were we to reform all the absurd 

 denominations existing in science, no material good would be procured, and immense 

 confusion, on the other hand, would ensue. If, therefore, a name is not essentially 

 objectionable, it should not be changed, and we will therefore retain the old name Oholus, 

 which has become current in science.^ I have already stated the reasons for not 

 admitting the genus under consideration into the same family with Siphonotretaeae, and 

 for placing it, on the contrary, close to Linpda?' 



Geol. range. — Oholus is one of the most ancient forms, abounding in the lower Silurian 

 beds of Russia, and in the Wenlock Shales of England, above which no authenticated 

 example has been as yet observed.^ 



Examples: 0. ApoUinis, Sch. {^=A. polita, Kut.) ; sculpta, Kut., sp. ; Davidsoni and 

 transversa, Salter, sp. 



1 See also Mr. Morris's observations, in the An. and Mag. of Nat. Hist., vol. iv, 2d ser., 1849. 



2 I take this occasion to express my sincere thanks to Dr. Volborth and Professor Kutorga for having 

 enabled me to examine, and kindly presented me with an extensive series of examples of this and other 

 Russian forms. 



■^ Having recently been requested by Mr. Salter to examine some curious impressions and internal 



casts derived from the Wenlock shales of 

 Walsall, Parker's Hall, Dudley, and Wool- 

 hope, with a view of ascertaining the 

 genus to which they belonged, I was not a 

 little interested to find, after a minute com- 

 parison with an extensive series of Obolus 

 Apollinis and sculpta, that our English 

 Upper Silurian Fossil really belonged to 

 the Russian genus, which had not hitherto 

 been noticed above the Lower Silurian 

 Rocks of Russia. Our British specimens 

 appear to belong to two distinct species, 

 and attained considerable dimensions, one 

 of them is of a transversely oval shape, and 

 appears to have been a thin shell, while 

 the other is more circular, and appears 

 from the depth of the muscular and other 

 impressions to have been a very thick shell. 

 Mr. Salter will shortly describe the two 

 forms under the names of O. Davidsoni 

 and O. transversa, and in order to facilitate 

 the comparison of the different muscular 

 impressions, I have accompanied these few 



Fig. 53. 



Fig. 52. 



Fig. 50. 



Fig. 54. Fig. 55. 



Fig. 51. Obolus Apollinis, /com Ruma. 



52. Interior of the ventral valve. 



53. O. transversa (Salter). 



54. 0. Davidsoni (Salter), Dudley, interior of ventral valve. 



55. Interior of dorsal valve. 



56. Side view of both valves. 



observations by woodcuts illustrating both the Russian and British species 



