100 GUIDE TO THE FOSSIL INVEKTEBEATE ANIMALS. 



Gallery (Fig. 46, 4), and by Meyeria in the Lower Cretaceous series. 

 VIII. 5?lie earliest representative of Palinuridse appears to be 

 Table-eases Pcdinurina from the Lower Lias of Lyme Eegis. Following 

 21, 20. this in Upper Cretaceous beds and in the English Eocene 

 is Podocrates \_Thcno2^s\ scarcely to be distinguished from 

 Wall-case Linuparus now living in Japanese waters. Oancrinus, also a 

 12c. Solenhofen genus, possibly led to the Scyllaridse, which are 

 Table-case represented in the English Gault and London Clay by 

 21. Scyllaridia, and in the Chalk by Scyllarus. 



The true lobsters and crayfish are examples of the tribe 

 Astacidea. These forms have pincer-claws on the first 

 Table-case three pairs of legs, and the first pair is very large. Already 

 21- in the Lias we meet with Eryjiia, which is also found with 

 Wall-ease Psendoastacus in the Solenhofen stone ; these two, especially 

 •'■2c- the latter, are very like the freshwater crayfish. In the 

 Table-cases Chalk, Enoplocytia is fairly common and strikingly lobster- 

 21 and 20. g^-^t Hoploimria, found in Cretaceous and Tertiary 



rocks, is even more closely allied to the modern lobster 

 {Homarus) and its near relation Nephrops, of which the 

 N"orway lobster is a familiar example. 



Ccdlianassa is a characteristic genus of the tribe Thalas- 

 sinidea, burrowing forms, with a soft, loosely built body. 

 In recent species of the genus the end segments of the first 

 leg with its pincer-claw are greatly enlarged and flattened 

 for shovelling ; but this is only in one leg of the pair. From 

 Table-case the Kimmeridge Clay of England comes Callianassa isochela 

 in which this flattened claw is not so disproportionately 

 enlarged and is found in both legs of the first pair; the 

 preservation of the abdominal segments in this fossil 

 suggests that they were not so thin-skinned as in later 

 Wall-case forms. In Cretaceous and Tertiary rocks the characteristic 

 12c. claws are found, but not the abdominal segments as a rule. 



We come now to the Brachyura. The typical crabs of 

 the present day difler from the decapods thus far described 

 in the following characters among others : the abdomen is 

 short and so bent up under the body that it is quite or 

 almost invisible from above ; its last segment bears no tail- 

 appendages ; there are at most nine pairs of gills ; the maxil- 

 lipeds of the third pair are broad and flattened, so as to cover the 

 other mouth-parts ; the front feelers are set in cavities formed 

 by partitions that connect the front margin of the carapace 

 with the hard parts of the under surface ; the whole body is 

 rarely longer than broad. There is, however, a primitive 

 tribe of Brachyura, the Dromiacea, in which these characters 



