300 H. L. Hawkins — The Lantern of Ferischodomus. 



should be found distributed over so vast a geographical area among 

 the living fauna of our globe. They may indeed justly claim to be 

 considered as amongst the oldest living races and the marvels of the 

 animal world. 



It is true that the other great group to which they are so closely 

 related, the Eurypterida, has passed away, not having survived 

 beyond the Carboniferous epoch ; but as this group certainly appeared 

 earlier on life's scene, it doubtless impressed its mark upon other 

 types of Arthropoda, and quite possibly was the great ancestor of the 

 Scorpions and King-crabs in earlier Cambrian times. 



IV. — The Lantern of Pebischodomvs. 



By Hebbert L. Hawkins, M.Sc, F.G.S., Lecturer in Geology, University 

 College, Reading. 



SOME years ago Mr. D. M. S. Watson and I collected, from the 

 Carboniferous Limestone of Clitheroe, Lancashire, a considerable 

 series of Echinoids. One slab of the limestone (measuring 16x12 cm.) 

 is covered by a great number of disjointed plates and other skeletal 

 fragments of a large Perischodomiis, probably P. hiserialis, M'Coy. 

 Dr. R. T. Jackson refers to the specimen {Phylogeny of the Echini, 

 p. 406), and, as the jaw fragments show features not hitherto 



Figs. 1, 2. — Perischodomus hiserialis (?). Alveolar and interpyramidal views 



of maxillae. 



described for the genus, it seems advisable to give a brief account 

 of it. The preservation of a compass is a point of special interest, 

 as these delicate structures are known in very few cases in the 

 fossil state. 



Ilaxillce (Figs. 1, 2). — Fragments of eight of the ten maxillae are 

 preserved, three of them being very well shown. The two figured 

 examples show the interpyramidal and alveolar surfaces completely. 

 They agree absolutely in measurements, as do all the other fragments 

 as far as can be ascertained. Symphysial margin 16, dental slide 16, 



