THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE III. VOL. VII. 



No. XII.— DECEMBER, 1890. 



OZR-IO-XIET.A.Xj abtigles. 



I. — On a New British Isopod (Ctclosph&roua trilobatum) from 

 the Great Oolite of Northampton. 



By Henky Woodward, LL.D., F.R.S., F.G.S. 



(PLATE XV.) 



MR. THOMAS JESSON, B.A., F.G.S., of Great Houghton House, 

 Northampton, was lately so fortunate as to discover in the 

 Great Oolite of that county, a new and most interesting example of 

 an Isopodous Crustacean, which, by his kindness, I am permitted to 

 figure and record in the Gkological Magazine. 



The last-described British Isopod was obtained from the Upper 

 Greensand of Cambridge, and made known by Mr. James Carter, 

 F.G.S., in this Magazine. 1 In his paper Mr. Carter gives a careful 

 resume of our knowledge of the species of this order which have 

 hitherto been found in a fossil state, both British and Foreign, and 

 it will therefore be sufficient, for our present purpose, to refer the 

 reader to that admirable summary. 



The specimen, which forms the subject of this article, was found 

 imbedded in compact white crystalline limestone ; only the upper 

 surface of the cephalon, the body-segments and the telson being 

 exposed (see Plate XV. Fig. la). About one-half of the fossil, 

 consisting of the cephalon and the anterior thoracic segments, has 

 the outer crust or shell preserved ; the posterior segments, the 

 abdomen and telson are seen as a sharp cast of the animal in the 

 fine calcareous matrix. The margins of the cephalon, the segments 

 and telson have suffered considerably in the process of removal 

 from the parent-rock in which they had been enclosed, thus leaving 

 much to be desiderated before we can obtain a complete and 

 satisfactory knowledge of the fossil. 



The epistomial plate, together with traces of the antennules and 

 antennaj, can be made out in front of the cephalon (PI. XV. Fig. Ic) ; 

 also the basal portion of the left uropodite on the side of the telson. 



A careful comparison of Mr. Jesson's specimen with several 

 recent and fossil forms, has satisfied me that it should be placed in 

 the Isopoda, and in the Family Sph^eromid^;, of which 1 here subjoin 

 a brief diagnosis, summarized from Messrs. Spence Bate and J. 

 O. Westwood's excellent work. 2 



1 See Geol. Mag. 1889, pp. 193-196, PL VI. Figs. 1-7. 



2 A History of the British Sessile-eyed Crustacea, by C. Spence Bate and J. 0. 

 "Westwood, 1SGS, in 2 vols. ; vol. ii. p. 398, etc. 



decade III. — VOL. VII. — NO. XII. 34 



