558 MR. J. CARTEK ON THE 



to the monodactylous genus OlypJiea as at present defined ; nor can 

 I assign it with any degree of confidence to its proper genus. 



The points of special interest to which I wish to direct attention 

 are: — 



1. That the decapod Crustaceans of the Oxford Clay are repre- 

 sented in this country by the occurrence of a larger number of 

 species than had been previously determined. The comparative rarity 

 of this class of fossils in the British rocks contrasts strikingly with 

 their remarkable abundance in a formation of a somewhat later date, 

 the Lithographic Slates of Solenhofen &c. The degree to which 

 this absence implies previous non-existence scarcely admits of deter- 

 mination with our present knowledge of facts. 



2. That the Oxford-Clay forms belong almost exclusively to the 

 Macrurous type, the Anomura being very scantily represented, and 

 the Erachyura still more so. 



This fact is of biological interest as marking a progressive develop- 

 ment from the lower to a higher type. The rarity of Brachyura 

 during the Jurassic era contrasts with their preponderance over the 

 Macrura during the Cretaceous period ; and they probably outnumber 

 the Macrura existing at the present time in the proportion of three 

 to one. I believe they do not occur at all in the Solenhofen beds, so 

 prolific of tbe Macrurous forms. 



The only species described in this paper which can be referred to 

 the Brachyura is Goniochirus cristatus ; and M. Etallon suggests that 

 this, as also the allied genus Orhomalus, may probably be proved 

 to be Anomurous by the discovery of better-preserved specimens. 



EXPLANATION OF PLATE XVI. 



Fig. 1. Eryon sublevis, nov. sp. Natural size. St. Ives. 



2. Erymob Mandelslohi, Meyer, sp. Nat. size. St. Ives. 



2 a. — . Chela found in situ with the carapace, fig. 2. 



2b, c. . Other forms of chelae. 



3. Villersi, Moriere. St. Ives. Dactylopodite and portion of 



fixed finger of first pair of limbs. 



3a. . Propodite of another specimen. 



4. Georgii, nov. sp. Nat. size. St. Ives. Carapace resting on the 



right first limb, of which the dactyl, propos, carpus, and a portion 



of the meros are recognizable. 



4 a. . ^ — -. Chela of first pair. Nat. size. 



5. fulojiella, nov. sp. St. Ives. Propodite of first pair and portions 



of posterior limbs. Nat. size. 



5 a. . Enlarged. 



6. Glyphea hispida, nov. sp. Nat. size. St. Ives. 



6 a. . Distal portion of propodite of first pair. Enlarged and 



transverse section. 



7. Magila levimana, nov. sp. Nat. size. St. Ives. 



7 a. . Portions of first pair of limbs and of abdominal seg- 



ments. Enlarged. 



8. : dissimilis, nov. sp. Nat. size. St. Ives. 



8 a. . Chela and transverse section of dactylopodite. En- 



larged view. 



9. 9 a. Goniochirus cristatus, nov. sp. St. Ives. Chehc of first pair of 



limbs. Nat. size. 



