BRITISH FOSSILS. H 



And, lastly, I stated the results of the same inquiries still more 

 fully in my " Lectures on General Natural History/' published in 

 the Medical Times and Gazette for 1857. 



The evidence upon which the following attempt to give a con- 

 nected account of the structure of Pterygotus is based, is both 

 positive and negative. Numerous specimens testify to the existence 

 of certain characteristically formed parts, and to the arrangement 01 

 these in a definite order in the body of the animal, so that its 

 general configuration may be very confidently restored. On the 

 other hand, the large number of fragments of many species of 

 Pterygotus which have been inspected, without revealing anything 

 new, leads me to entertain a strong impression that no structures 

 of any very great importance remain to be discovered. 



With regard to the nature of the positive evidence, I may 

 premise that of the fifteen distinguishable species of the genus, 

 the remains of only five, viz., anglicus, acuminatus, punctatus, 

 perornatus, and bilobus have yielded facts of capital importance in 

 a structural point of view ; I shall, therefore, confine myself to 

 these species, referring the reader to the systematic portion of this 

 monograph for information respecting the rest, and indeed for all 

 details of no anatomical importance concerning even these. . 



Of the species named, the only entire specimens yet discovered 

 belong to P. bilobus, but the large size and comparatively perfect 

 condition of the detached parts of P. anglicus, added to the fact 

 that the genus was originally founded on this species, render it 

 convenient to commence with a description of them. 



1. The Carapace. In Lord Kinnaird's collection there is a large 

 flattened plate, figured in Plate III. fig. 1, which appears to have 

 possessed a trapezoidal form when perfect, but is at present very 

 irregular (though by no means distorted), one of its angles and a 

 considerable portion of the margin of the longest side having been 

 broken away. The shortest or anterior side is very slightly convex, 

 the opposite and parallel longest side is a little concave; that 

 lateral margin which is entire is nearly straight, but is rounded off 

 where it joins the posterior edge. The surface of the fossil is slightly 

 concave, and exhibits neither sculpture nor distinct granulation, but 

 it is marked by a great number of sinuous elevations and depres- 

 sions. At the outer extremities of the anterior edge are two large 

 and deep depressions of an oval form, having their long axes directed 

 obliquely forwards and inwards. 



The surface of each concavity presents a great number of minute, 

 but regular and close-set depressions (Figs. 1 a, 1 6), which appear 



