406 J, W. Jackson — Coal-measure Arthropods. 



is a much more slender one than the examples from the Lancashire 

 and Staffordshire Coal-fields. 



The second form of Orthoceras belongs to Professor de Koninck's 

 division " Orthocerata, 2nd Annulata ", as the surface is ornamented 

 with numerous fine concentric rings. It is a much more robust 

 species than the other, recalling Orthoceras cinctum, Sow., but the 

 material available is too imperfect for accurate determination. 



VI. — Notes on Two Arthropods from the Lancashire COAL- 

 MEASURES. 



By J. Wilfrid Jackson, F.G.S. 



SOME time ago the Manchester Museum purchased a selection of 

 Coal-measure Fishes from trie executors of the late Mr. John 

 Ward, of Longton, and included with these were gutta-percha casts 

 of two species of Arthropods. These were mounted on wooden tablets 

 covered with green paper, one specimen being labelled: " Limulus 

 trilobitoides, Buck. (Bridgeivater Treatise, vol. ii, pi. xlvi, fig. 3). 

 Roof of the Upper Bent Mine, Middle Coal-measures, Hunt Lane, 

 near Oldham. Original in the cabinet of E. W. Binny, Esq." The 

 other: u Zimulus rotundatus, Prest. Coal-measures, Oldham." 



The first-mentioned species (now recognized as Belinurus lunatus, 

 Martin, sp.) is recorded by Salter in the Geological Survey memoir, 

 The Geology of the Country around Oldham (1864), p. 63, as 

 follows: "Limulus trilobitoides, Oldham (Manchester Geological 

 Museum)." Bolton in his "Palaeontology of the Lancashire Coal- 

 measures " 1 also repeats this record, and adds: "The original specimen 

 was deposited in the Natural History Museum, Manchester, but has 

 disappeared." 



No horizon is given by Salter for this species, nor does it appear to 

 have been recorded since from any Oldham horizon ; the fact, there- 

 fore, of the cast possessing full details as to precise locality and horizon 

 is of particular interest. 



It is much to be regretted that the second species (now recognized 

 as Prestivichia rotundata, H. Woodw.) does not possess a like amount 

 of information as to its horizon, etc. It does not, however, seem 

 improbable that it is referable to the same horizon as Belinurus lunatus. 



I 



VII. — On the Layers of the Molluscan Shell. 



By A. K. Horwood (Leicester Museum). 



AM glad that my short article 2 dealing with the occurrence of 

 aragonite in the Middle Lias has evoked some interest. Professor 

 Grenville Cole, 3 who notices (with Mr. 0. H. Little) this paper, has 

 evidently delved deep, and I only hope that the publication of 



1 Trans. Manch. Geol. Soc, vol. xxviii, p. 601, 1905. 



2 "On the Occurrence of Aragonite in the Middle Lias of Leicestershire; 

 with some remarks on the calcareous character of the spinatus beds " : 

 Geol. Mag., 1910, p. 173. 



3 "The Mineral Condition of the Calcium Carbonate in Fossil Shells": 

 ibid., 1911, p. 49. 



