Mr B. N. Peach on the Occurrence of Pteryyotus, etc. 349 



chelate palpi these tail segments are the strongest parts of the 

 animal's test, and therefore the most apt to resist decay. The 

 tail was highly muscular, containing few of the viscera except 

 the straight intestine, so that the test of that part required a 

 great deal of stability. This was obtained by the bulging 

 and arching of each segment, by the internal llange, the 

 dorsal keel, and embossing of the test. 



The Limuloid referred to in the title of this paper is the 

 cast of a Limulus-like creature which was got by C. W. 

 Peach from the Caithness flags, near John o' Groat's House, 

 where the highest beds of the Lower Old Red Sandstone 

 which are to be found in Caithness occur. Though merely a 

 cast, and altogether not over an inch and a half in length, 

 and not quite so broad, it is sufficient to show the impression 

 of a large carapace, which has been divided into several 

 raised and depressed areas paralleled on each side of a mesial 

 line, though now somewhat distorted by pressure. This is 

 flanked laterally by the usual recurved horns at the posterior 

 angles. Behind the carapace are the impressions of seven 

 body segments, each of which has a central lobe and pointed 

 epimera, ending in recurved spines. x\t the place where the 

 tail spine occurs in Limulus and Bellinurus there is a depres- 

 sion in the matrix such as could be produced by a similar 

 one. From the manner in which the central lobed portion 

 of the abdomen is deeply impressed, there is every reason to 

 believe that the segments were movable on each other, and 

 not coalesced into an abdominal shield as in Limulus. The 

 affinities therefore of the creature are more with Bellinurus 

 than any other known Limuloid, though the specimen is too 

 hazy to assign even a generic name to. The accompanying 

 outline sketch shows the parts that have been made out after 

 a lengthened study, which leaves no doubt of the specimen 

 being the cast of a Limuloid (see PI. VIL, Fig. 4). 



The specimens of Pterygotus and the Limuloid cast have 

 been described mainly to draw the attention of geologists to 

 the fact that the remains of such creatures do occur in the 

 Caithness and Orkney rocks, so that collectors may be 

 induced to look particularly for them, as there is a peculiar 

 interest attaching to the history of this group of animals. 



