On the Scattered Skeletal Remains of Holothuroidea. 195 



AcMstrum Nicholsoni, Sp. nov. — (PL V., Figs. 1, 2, 5, and 6). 



Sp. Char. — Margin of plates undulating ; perforations plain, 

 non-serrate or pectinate. Anchor hooks plain, or slightly 

 serrate (?) ; distal end a little enlarged and perforated by a 

 hole or eye. 



Ohs. — The plates are usually of a more or less oval form, 

 sometimes becoming irregular. The perforations vary from 

 something under a dozen to as many as forty-one, and per- 

 haps more. The marginal holes in some examples are smaller 

 than those over the body of the plate, in other examples 

 they are crowded to one end. Both these characters are met 

 with in Synapta constantly, but here they are very variable and 

 inconstant. I have met with one or two examples amongst the 

 fossils in which the large perforations are very much reduced 

 in number, and all clustered towards the centre of the plate. 



Omitting for a moment the presence of the one-fluked 

 anchors these plates show a much greater affinity with some 

 forms of the HolotMhria and Cncnmaria groups than they do 

 with Synapta. 



I have much pleasure in associating the name of my friend 

 and co-worker. Professor H. A. Nicholson, M.I)., with these 

 plates. 



The above description does not include the plates with the 

 smaller perforations. They have already been described in 

 the general body of the paper, and, with the exception of the 

 much more numerous holes, smaller size, and more circular 

 outline, they agree with the former. They may be only a 

 variety, or plates answering to the " miliary granules " in 

 A. Nicholsoni, or, on the other hand, quite a distinct species. 



The average size of the plates in A. Nicholsoni is -gVth of an 

 inch in their longest diameter. The largest perforations are 

 2^th of an inch in diameter. The hooks have an average 

 length of '0232 inches. 



Loc. and Horizon. — Eiver Avon, below Kinneil Mill, near 

 Linlithgow ; shale above the Dykeneuk, or Gair Limestone, 

 Up. Carboniferous Limestone Group. Woodend Quarry, near 

 Fordel, Fife ; shale above a limestone, Lower Carboniferous 

 Limestone Group. 



