XCiv PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 896, 



they are placed below the frontal border of the head, at the base of 

 the antennae. 



I formerly entertained a very strong conviction that it would be 

 possible to show the derivation of the Isopoda by direct descent 

 from the Trilobita ; but the former have so very constant and 

 definite a number of 21 body-segments — as indeed is the case in the 

 Malacostraca generally — (namely, 7 somites in the head, 7 in the 

 thorax, and 7 in the abdomen), whereas in the Trilobita (as is the 

 case with the Entomostraca generally) the number varies greatly, 

 from 4 or 5 up to 28 somites in the body, that I feel I must recant 

 and give up this heresy at once, lest I should be excommunicated 

 by some later Carcinologist, and my effigy and papers burnt, if not 

 my person. 



It is probable that the Isopoda date back to the Devonian, for I 

 have, in 1870, described, under the name of Prcearcturus gigas, a 

 form which appears to be a portion of a huge Isopod from the Old 

 Red of E-owlestone, Herefordshire. 



Portions of similar large Arthropods, which have been named 

 Arthropleura ferocc, by Salter, and A. armata, by Jordan, have been 

 obtained from the Coal Measures of Manchester, of Pifeshire, of 

 Padstock, Somerset, and from Saarbrucken,Bhenish Prussia, so that 

 we may justly hope soon to obtain a fuller knowledge of the true 

 characters of this remarkable animal. 



The anomalous form, known as Bostrichopus antiquus (Goldfuss)' 

 from the Devonian of Nassau, may perhaps be placed here, as 

 possibly related to the Munnopsidse. 



Several species of Palceocaris (P. scoticus, P. Bumettii, and P. ty- 

 pus) have been described from the Coal Measures of Manchester, of 

 Scotland, of Bohemia, and of Grundy County, Illinois, U.S.A. ; from 

 this last-named locality another genus, Acanthotelson Stimjpsoni, 

 closely resembling Palceocaris, has also been obtained by Messrs. 

 Meek and Worthen. These larva-like forms were relegated, by the 

 late Prof. J. D. Dana, to a group holding an intermediate position 

 between the typical Isopoda and the Amphipoda, for which he pro- 

 posed the name ' Anisopoda.' 



Isojpodites triasicus, Picard, from the Muschelkalk of Thuringia, 

 is somewhat doubtful. An undoubted Sphceroma-like Isopod, from 

 the Great Oolite of Northampton, has been described by me under 

 the name of Cyclosphceroma trilobatum, in 1890. 



The Lithographic Stone of Solenhofen, Bavaria, has yielded two 

 genera of Isopodous Crustacea, described in 1839 by Count Miinster y 



