from Queen's Count ij, Ireland. 113 



2. Bdinurus arcuatus, n. sp., Bally. Bilboa Colliery, Queen's 



County, Ireland. 

 3. RegincB, n. sp,, Baily. Bilboa Colliery, Queen's County, 



Ireland. 

 4. anthrax, Prestwich, Geol. Trans, vol. v. pi. 41. figs. 1-4, 



Coalbrook Dale. 

 5. rntundus, Prestwich, ibid. Coalbrook Dale and ? Bilboa 



Colliery, Queen's County. 



The discovery of these peculiar Coal-measure Crustacea in 

 Ireland, with associated shells and plants corresponding so re- 

 markably with those found in similar deposits at Coalbrook 

 Dale in Shropshire and other parts of the Midland counties in 

 England, is a point of great palseontological interest, showing 

 their distribution over a wide area, and indicating the prevalence 

 of the same conditions in both countries, although at localities so 

 widely distant. The great differences observable in some parts 

 of their structure to that of the more recent and living forms of 

 Limulus may be accounted for by the wide interval which sepa- 

 rates the Coal-measure strata in which their remains are found 

 from the Upper Jurassic formation, where those of true Limuli 

 first occur. There are, however, certain points in their structure 

 analogous to that of Limulus, which they somewhat resemble in 

 their general form and in being provided with a tail-spine that 

 was most probably (although the articulation is not clearly 

 shown), like that oi Limulus, capable of mobility; on the other 

 hand, as we recede in time, we find intermediate forms, such as 

 Pterygotus and Himantopterus, connecting them with the Trilo- 

 bites, to which they are also allied by the moveable nature of 

 their body-segments, and in other particulars. We have, there- 

 fore, in these Coal-measure Crustacea such a modification of 

 structure as may be considered sufficient to constitute them a 

 distinct genus, and show them to be a link in the chain leading 

 from the important group of Trilobites, so characteristic of the 

 Palseozoic rocks, to the Oolitic Limuli, in which the whole body 

 is covered by a double shield, the segments of the abdomind 

 portion being merely rudimentaiy and immoveable, like those 

 of the existing species. 



As to the question of the freshwater or marine habitat of these 

 Crustacea and their associated fossils, I am inchued to the 

 opinion that the deposits in which they occur were of freshwater 

 or estuary origin, from the abundance of small shells like Unio, 

 and others very similar to the freshwater Mytilus {Dreissena) 

 polymorpha, accompanied by the remains of succulent or marshy 

 plants. This opinion corresponds with the obser\ations of 

 Martin and Prestwich. Other theories have been advanced 



