ELONICHTHYS AITKENI. 7M 



The length of the pectoral fin (PI. XVI, fig. 2) is about two thirds that of the head ; 

 its principal rays are uiiarticulated for about one third of their length. The ventrals are 

 badly preserved in the specimens which I have seen, but their position seems to have 

 been halfway betweeu the pectorals and the anal. The dorsal, well shown in the 

 same figure, is situated opposite the iuterval between the ventrals and the anal ; both 

 dorsal and anal fins are pretty large, and of the usual triangular-acuminate shape; theii; 

 rays are delicate and slender, distantly articulated and smooth, save that now and then 

 a single longitudinal furrow is seen, especially just before bifurcation sets in. The 

 caudal is com|)letely preserved in the specimen depicted in PI. XVI, fig. 1 ; it is large 

 and deeply cleft ; the articulations of the rays of the lower lobe are a little closer than 

 those of the dorsal ; in the upper lobe the joints become so short as to look nearly 

 square-shaped. 



Observations. — This exceedingly fine species was described by myself in 1886, and 

 named after the late Mr. John Aitken, of Bacup, Lancashire, to whose collection the 

 beautiful specimen represented in PI. XVI, fig. 1, belonged. I had, however, previously 

 recognised the fish as new from specimens from Burnley belonging to Mr, George Wild, 

 of Ashton-under-Lyne, and with which I also identified specimens from Stanton in Derby- 

 shire in the British Museum, in the Museum of Practical Geology, and in the collection 

 of the late Mr. E. W. Binney. On these specimens, all from the Lower Coal Measures 

 of Lancashire and Derbyshire, the above description has been founded, but there is one 

 in the British Museum collection from the " Culm " of Instow, Devonshire, referred by 

 Dr. Smith Woodward in his " Catalogue " to the same species, and which deserves a 

 few special remarks. This specimen is represented in PI. XVII, fig. 7, and is an 

 extremely sharp impression of the head and anterior part of the body, showing with the 

 greatest distinctness the opercular bones, the orbit and suborbitals, tlie maxilla and 

 mandible, the branchiostegal rays, the infra-clavicidar })lates, and })ortions of both 

 pectoral fins, as well as the anterior scales of the flank and belly. The ornament of the 

 scales resembles closely that of the typical E. Aitkeni, but it is to be noted that the 

 striae on the mandible, instead of proceeding more or less horizontally as in fig. o, pass 

 obliquely from below upwards and forwards towards tlie dentary margin ; further, that 

 the maxilla is differently shaped from that represented in fig. 4, being lower and 

 narrower, and having the posterior margin more oblique and not angulated in the 

 middle. There is therefore souje presumption that we have here to deal with a difi'erent 

 species, but after my experience as regards the variability of E. Robisoni, I think it 

 safer to defer for the present any decision on this question. 



In the Edird:)urgh Museum there are two specimens from the roof-shale of the 

 " Four Foot " coal (Upper Carboniferous) at Niddrie, near Edinburgh, which I refer to 

 this species. One consists only of a few dislocated bones and scales ; the other is a 

 pretty entire fish, five inches in length, but having the scales much broken and jumbled 

 up, so that their markings are not very well seen. So far, however, as their sculpture 



