On the " Seraphim " and its Allies. 231 



which we shall presently refer to, it is evident Mr. Page's 

 collection contained more perfect specimens of P. acuminatus 

 than the officers of the survey were acquainted with, and which 

 have only been surpassed by specimens very recently obtained 

 for the national collection by Mr. Bryce M. Wright (36, Great 

 Eussell Street), and collected by Mr. Robert Sliinon, of Les- 

 mahagow. That figured in our plate is perhaps the best example, 

 and represents an almost entire specimen of Pterygotus* acumi- 

 natus, Salter (so called from the peculiar pointed form of the 

 tail-joint) . It is only one-third the natural size, the original 

 being twenty-seven inches in length. The largest individual of 

 this species I am acquainted with would have measured, if 

 entire, more than three feet in length, and nine inches to one 

 foot across its widest body-segment. The smallest perfect 

 specimen of this species in the British Museum measures six 

 and three-quarters inches in length, and one inch across its 

 widest segment. 



P. acuminatus is the largest species found at Logan Water. 

 A restoration hi correct proportion to the size of the fragments 

 of the great Pterygotus anglicus, from the Lower Old Red 

 Sandstone of Perthshire and Forfarshire, would give us a 

 creature measuring from six to eight feetf in length, and 

 more than a foot wide ! It is an interesting fact to notice that 

 the largest crustacean living at the present day is the Inachus 

 Kcempferi of De Haan, from JapanJ (a brachyurous or short- 

 tailed crab, nearly related to Maia sauinado of our own 

 shores) ; whilst the Pterygoti are not only related to the lower 

 and more simply organized living Crustacea, but those also 

 winch are least in the scale in point of size.§ 



It needs but a slight acquaintance with the Crustacea to per- 

 ceive that the Pterygotus is a most remarkable and anomalous 

 creature. The head alone appears to possess any separate 

 organs, and these are adapted at once to serve the multifarious 

 purposes of feeling, locomotion, prehension, and mastication. || 



The oblong square carapace^" (A 1), with its large sessile eyes 

 at the anterior angles; the heart-shaped plate in the centre (e), 



* The genus Slimonia of Page, 1856, was founded upon this species, although 

 not properly constructed or defined. 



f Mr. Salter is of opinion that P. prohlematicits from the Downton sand- 

 stone, and gigas from the Ur. Ludlow Kock, attained dimensions fully as large. 

 See his re-t oration of P. anglicus in Murchison's Siluria, new edition, 1859, 

 foss. 21, f. 1. 



X It is not the size of the carapace for which this crab is remarkable, but the 

 extraordinary length of its limbs ; the fore-arm measuring four feet, and the 

 others in proportion; so that it covers about twenty-five square feet of ground. 



§ Honourable exception must, however, be made in favour of Limuhis moluc- 

 canus (the great King crab) of China and the Eastern seas, which, when adult, 

 measures one and a-half feet across the carapace, and three feet in length! 



|| The feet in some Crustacea also serve the office of branchiee. 



IT Not seen in silu in the largo specimen, but figured separately A 1. 



