8 BRITISH FOSSILS. 



with Agassiz's idea of their position ; while, in fig. 543, the 

 epistoma is represented as the carapace, and a transversely 

 elongated eye is made to appear on either side of its median lobe, 

 about midway between the 'middle line and the margin! The 

 chelate appendages are made to arise from behind this supposed 

 carapace, and are succeeded by two or three pairs of articulated 

 appendages. In short, wherever Professor M'Coy departs from 

 M. Agassiz's conception of the structure of Pterygotus, the altera- 

 tion is not an improvement. 



In 1852 Mr. Salter published a " Description of the Pterygotus 

 problematicus" in the "Quarterly Journal of the Geological Society," 

 in which the following passage occurs : 



" It is probable that there are numerous species of the genus in 

 the old rocks. Fragments, with the characteristic markings, occur 

 in Upper Silurian shale at Gaspe', Lower Canada ; and portions 

 of the limbs of a Bohemian species have been figured by the 

 late M. Corda as the feet of Brontes, a genus of Trilobites." 



Mr. Salter expresses his concurrence in the systematic views of 

 Professor M'Coy. 



The Report of the British Association for 1855, " Transactions of 

 the Sections," (pp. 89-91), contains the abstract of a paper by Mr. 

 D. Page, " On the Pterygotus and Pterygotus Beds of Great 

 Britain." The following passages show what views were then 

 entertained by Mr. Page with respect to the structure of these 

 animals : 



" The Pterygotus, of which there appeared to be three distinct 

 species, the gigantic problematicus, the anglicus, and the punc- 

 tatus, was altogether different in its general structure' from any 

 crustacean living or extinct. The portions chiefly found (and of 

 these capital specimens are in the collections of Lord Kinnaird, 

 the Watt Institution, Dundee, &c., all originally from Balruddery,) 

 were the frontal cephalic shield, the posterior cephalic or thoracic 

 shield, with its lunar-like epimera, the abdominal segments, gene- 

 rally from seven to eleven in number, the huge prehensile claws 

 with their curious denticulated edges attached to limbs of great 

 length, the shorter swimming limbs with their paddle-like ap- 

 pendage, and several semi-oval detached plates which evidently 

 belonged to the breast or under side of the animal. Putting all 

 these portions in place as nearly as could be determined, we had 

 a huge lobster-like crustacean, but only lobster-like in general 

 contour, for in its true generic relations it belonged to no existing 

 family of the order. Partly phyllopod and partly psecilopod, in 

 its abdominal segmentation macrourous, and in its thoracic appa- 



