ARTHROPLEURA MAMMATA. 167 



With regard to the remaining fragments referred by Mr. Salter to Eurypterus mam- 

 matus (see PI. XXIV, figs. 4, 5, 6), I am in no little difficulty; for here again Mr. 

 Salter's description is borne out by his woodcut figures, but not by the specimens. 



For instance, he speaks of the peculiar "tear-drop" ornamentation along the hinder 

 margin of the segments, such as is seen in certain other fragments referred to Eurypterus 

 (see PI. XXVIII, figs. 16, 17, and 17 a). But in figs. 4, 5, and 6, these are really cracks 

 in the tissue, as correctly represented on our plate by Mr. Griesbach, and not raised 

 tubercular ornamentations thereon, as seen in the woodcut, p. 84 (figs. 4, G, and 7). 

 Mr. Salter himself says : 



" The remaining pieces are evidently parts of a great Crustacean, and almost certainly 

 belong to this one, for they have the same ornaments on the hinder edge ; but they differ 

 remarkably by having a curious set of short, wavy, interrupted ridges (or furrows, it is 

 impossible to say which) lying transversely to the length, and which are equally distributed 

 over the whole segment. They are not all of the same size, small rounded ridges being 

 mixed with those of a more linear shape." 



I carefully studied these fragments, and also submitted them to the examination of 

 my colleague, Mr. William Carruthers, E.R.S., who has devoted himself specially to the 

 study of fossil plant-remains, hoping that he would accept them as parts of some plant, 

 like Calamites or Knorria ; but for some time he was unable to do so. I was therefore 

 obliged to treat them as animal, and probably Crustacean, although I could not compare 

 them (like figs. 2 and 3) with any other form belonging to the order ; for the scale-like 

 ornamentation so characteristic of Pterygotus and Eurypterus is altogether wanting, nor 

 could I detect any evidence of spines such as are preserved on fig. 2. 



Fortunately at this juncture a portion of an undoubted plant-stem from the Ironstone 

 of the English Coal-measures, which Mr. Carruthers had laid aside for examination, 

 turned up, and furnished evidence of markings identical with those exhibited on figs. 4, 5, 

 and 6 of PL XXIV, so that there is no longer any reason to doubt their vegetable origin. 

 Mr. Carruthers has very kindly drawn up the subjoined account of these remains, which 

 may now be considered as disposed of in a satisfactory manner. 



The remaining specimens (figs. 2 and 3, PI. XXIV) will be retained to represent Mr. 

 Salter's species, which we refer provisionally to M. Jordan's genus as Arthropleura 

 mamwata, Salter, sp., about the affinities of which we cannot at present speak with any 

 degree of certainty. 1 



1 Just as this sheet was passing through the press I received two additional contributions to Salter's 

 Eurypterus {Arthropleura) mammatus. The first is a very curious compressed fragment of what appears to 

 be the sternum of the thorax of a Brachyurous Decapod from the Coal-measures near Manchester, sent me 

 for examination by W. Johnston Sollas, Esq., of St John's College, Cambridge. 



The other consists of three tuberculated epimeral pieces so exactly resembling that marked p in our 

 fig. b, Woodcut 55, p. 166, that, except for the variation in the wart-like tubercles, two of tlieru might at 

 once be mistaken for Jordan's type. There is the same deep groove in each, the same falcate border, the 

 same admixture of large and small tubercles upon its surface occupying relatively the same positions. The 



