POWRIE — FOSSIL FISH FROM THE OLD RED SANDSTONE. 337 



including tlie tail-segment, is three feet nine inches, and it measures 

 very nearly twelve inches across at its greatest breadth. Making a 

 fair allowance for the head, the creature must have been over four 

 and a- half feet long, and had thus formed a rather formidable 

 lobster-like animal when swimming in the waters of the primeval 

 world. It had not, however equalled in size the Pterygotus, to 

 which three tail-segments, very recently found in a quarry in 

 this immediate neighbourhood, had belonged, and which are now in 

 my possession. 



I here give a rough sketch 

 of this also very interesting 

 fossil. The dotted line marks 

 a portion which lifts clean 

 out from the matrix, leaving 

 a very fine cast of what I 

 consider to have been the 

 dorsal plates of these seg- 

 ments. The upper side of 

 this fossil seems to have 

 formed the upper portion 

 of one of the layers or beds 

 of the rock, and has the 

 sculpturings a good deal ob- 

 literated ; these are, however, ^ 

 beautifully preserved on the 

 under side, as also on the 

 cast. These markings are 

 much smaller on the caudal 

 than on the other plates, in- 

 creasing in size, but still 

 small, on the sub-caudal. 



The sub-caudal plate, and 

 that anterior to it, have 

 ridges along both the ven- 

 tral and dorsal surfaces, dif- 

 fering in this from some 

 other specimens of these 

 plates, which only show one 

 ridge. The caudal segment 

 where it joins the one above 

 extending to about one-fifth 



is of some considerable thickness 

 it ; this rapidly narrows, until, after 

 of its length, the upper and lower 

 sides seem to join and become one plate. It would thus appear 

 that the body of the creature had penetrated some little distance 

 into this segment. 'No appearance of any vent or anal opening is 

 found in these segments ; and as, from the state of preservation of 

 tliis fossil, had such an opening existed, it would have been in all 

 probability readily distinguishable, it affords strong negative evidence 

 against the existence of the vent in this part of the body of the 

 animal. The caudal plate is seven and a-half inches long by five 

 VOL. III. 2 u 



