CRITICAL BIBLIOGRAPHY. 25 



forms assumed by the shells are the result of crushing or imperfection, and 

 the general accuracy of the work may be judged from Taf. v, fig. 8, where the 

 impression of the external surface of a shell is correctly shown by the lines of 

 growth ; but the learned author has invented the anterior and posterior muscle- 

 scars on the outer surface of the shell, and found there the accessory adductor 

 scar wanting throughout the genus, and has described them in the text. Further, 

 certain swellings and prominences are said to be enlargements for the ovary, and 

 characteristic of the female sex. In the figure showing the hinge-plate of TJnio 

 crassidens the greater part is drawn from the imagination ; for the original speci- 

 men consists of two valves which have slipped on each other somewhat at the 

 posterior end, and shows only the posterior half of the hinge-line. I have been 

 unable to see the lateral anterior and posterior teeth described in the text and 

 figured, but this point will be discussed in detail hereafter. 



The total neglect (in three papers out of four) of all the work done on the 

 subject, both on the Continent and in England, is to be regretted; as, from a 

 careful comparison of the shells, I have no doubt that the species are to a large 

 extent the same as those previously described and figured by others. 



The following papers will not be all found in strict chronological order, for in 

 many cases there are several papers on the subject by the same author, and in 

 this case it has been thought better to group them together, so that each writer's 

 views may be presented in as concise a form as possible. 



1860. In the Geological Survey Memoir to Sheet 142, parts of the Counties of 

 Clare, Limerick, and Kerry, on p. 13 is a note by Mr. W. H. Baily in which is a 

 figure (fig. 4) of Myalina Foynesiana from the Coal-measures of Foynes Island, 

 co. Limerick. The specimen occurs in black shale with a Goniatite, and several 

 specimens of Posidonomya. The original specimen is in the Geological Survey 

 Collection at Dublin. In a note in the Memoir explanatory of Sheet 137, p. 12, 

 Mr. Baily says, " At Bilboa colliery in the four-feet bed of shale immediately over 

 coal No. 3 (three feet, or old colliery coal), which contained but few plants, 

 fresh-water or estuarine shells (Myacites) allied to TJnio, having both valves united, 

 were found in great abundance ; . . . with these were other species of bivalves, 

 having the shells compressed, belonging to the same genus and to Myalina. 



1860-78. The publication of the ' Acadian Geology ' in 1860 by Sir William 

 Dawson is important, as the name Naiadites is there given in the Supplementary 

 Chapter to embrace all those Coal-measure shells called Unio, Anodon, Modiola, 

 &c, by various authors. He describes eight species, six of which are figured. 

 In the second edition, 1868, and third edition, 1878, p. 204, the shells are again 

 figured and described with Salter's names given in brackets, the author advancing 

 good reasons for not accepting Salter's misnomer Anthracomya. 



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