1858.] BATE PEOSOPONISCUS. 137 



7. On the Fossil Crustaceajs^ found in the Magnesian Limestone of 

 Ditrhajm: hy Mr. J. Kiekby, and on a New Species of Amphipod. 

 By C. Spence Bate, Esq., F.L.S., &c. ( Communicated by Dr. H. 

 Falconer, F.R.S., F.G.S.) 



[Eead June 23, 1858.] 

 [Plate VI.] 

 In January, 1857, a paper by Mr. Kirkby was read before the 

 Geological Society*, on "some Permian Fossils from Durham," 

 in which a few fragments were described as the remains of an 

 extinct Crustacean. Some drawings of these were kindly submitted 

 to me previously to their publication. One series I regarded f as 

 being probably from the anterior portion of an Isopod; and the 

 remainder I considered as not belonging to the same animal, but as 

 parts of an Amphipod. 



I have recently (siuce the reading of this paper) been allowed, 

 through the kindness of Mr. Kirkby (to whom I applied in accordance 

 with a suggestion from the Council of the Geological Society), the 

 advantage of examining the original specimens of Prosoponiscus jpro- 

 hlematicus, together with others that have been discovered since the 

 publication of his paper. 



Having thus a favourable opportunity of reconsidering an opinion 

 which was given from an examination of drawings only, I have 

 been enabled to make out some points not portrayed in the 

 drawings, which enable me to arrive at a more satisfactory con- 

 clusion. The specimens are the anterior and middle parts of an 

 Amphipod ; and none belong to an Isopod, as I at first informed Mr. 

 Kirkby J. 



To show with any amount of certainty the correctness of this 

 hypothesis, it is necessary that I should demonstrate, iu recent 

 Crustacea, an approximation of structure to that of the fossil. 

 Assuming that, if certain known parts of an unknown animal agree 

 in character with those homologically the same in an animal that we do 

 Iniow, we have d priori a right to infer the undiscovered portion of 

 the one bears a corresponding relation to the remainder of the other. 



Commencing with the anterior fragments, there are specimens of 

 the cephalon with from two to four segments attached. The ce- 

 phalon is large, deep, laterally compressed, and slightly carinated 

 upon the dorsal surface, which carina is produced anteriorly into a 

 small point. The eyes are round and prominently elevated. The 

 posterior margin is slightly elevated. The inferior margin is stout 

 and strong ; and to this is attached part of an appendage, probably 

 that of a mandible (fig. 5, d). This little fact was overlooked in 

 the original drawings, probably from the close resemblance between 

 the colour of the fossil and that of the rock of which it is a part. 

 But this is more distinctly visible iu the specimen from which fig. 6 

 is taken (d). It therefore must follow that the eyes are not (as 



* Quart. Journ. Geol. Soc. vol. xiii. p. 213. 



t In the communication read June 23, 1858; this paper having been somewhat 

 modified since then by permission of the Council. 

 I Quart. Journ. Geol. Soc. vol. xiii. p. 214. 



