286 On the "Seraphim" and its Allies. 



* * * " I have also observed two forms of thoracic plates in 

 the other species (P. bilobus)"* 



We have given a figure of the upper portion of Eu/rypterus 

 remipes (De Kay), after Hall's Palaeontology of New York, lor. 

 cit., and by its side the same parts of P. acuminatus. P. bilobus 

 is a very much smaller species than P. acuminatus, and instead 

 of small, simple, and slender antennules,f it has large and 

 strong chela? or claws like the great " Seraphim," only on 

 a very much smaller scale. The succeeding organs in P. bilobus 

 are slender and unarmed, whilst those of P. acuminatus are 

 robust and spiny on every joint. The thoracic and tail-plates, 

 too, are quite distinct in shape, and so also is the cephalic 

 shield and the form of the eyes. Feeling as I did the importance 

 of these distinctions, amounting to far more than specific cha- 

 racters, I was much rejoiced at obtaining the independent sanc- 

 tion both of Messrs. Huxley and Salter to place it in a separate 

 genus, adopting for it the name proposed by Mr. David Page — 

 Slimonia acuminata.% 



The additions which we have been able to make (with the 

 kind assistance of Mr. Slimon) towards the completion of 

 Slimonia acuminata, consist in indicating another thoracic seg- 

 ment; so that the number of body joints is now the same 

 in Pterygotus and Eurypterus, increasing the number of organs 

 from three to five pairs, and demonstrating the true position 

 and character of the thoracic plate. Only one other point 

 of interest remains to be solved, namely, the position and 

 form of the respiratory organs, and upon this subject we are 

 not without good hope. 



We must now conclude our brief sketch of this remarkable 

 palaeozoic crustacean. Those who wish to enter more fully 

 into their history must refer to the monograph of Messrs. 

 Huxley and Salter, the Quarterly Journals of the Geological 

 Society, Professor Huxley's Lectures on Crustacea (printed in 

 the Medical Times and Gazette for 1857), and Hall's PalcBonto- 

 logy of New York for 1859. And all who desire to observe for 

 themselves, should bear in mind that the actual specimens can 

 bo seen and studied in our public collections at the British 

 Museum, and the Geological Survey, Jermyn Street. 



* Tlio median lobe of plate E, and an almost entire detached thoracic plate of 

 the form figured in woodcut K, were figured in Messrs. Huxley and Salter's 

 monograph ; but, not being found /'// situ, were attributed to the mouth as the 

 conjoined cpistoma and labrum. 



f The antcnnulcs of P. aottmiiiattu have their basal joints serrated, so as to 

 form the first pair of mouth organs. The antennulcs of /'. bilobus do not seem to 

 be famished with serrated hasal joints, a most important distinction. 



X Page's Advanced Text'Sook of Geology, 1856, p. 185, f. 3 j in compliment 

 to my friend, .Mr. Bobeii Slimon, of 1 .'•sni;ili;i<n>\\ , the di-eovcrcr of all the Lanark- 

 shire specimens. 



