100 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Cillery 46, 4), aiul by Mcycria in tiie Lower Cretaceous .series. 
The_ earliest repre.sentative of I’aliniiricl'e appears to be 
Table-cases Palinurina from the Lower Lias of Lyme l;efti.s. Followimr 
21, 20. i„ Upper Cretaceous beds ami in the Engli.sh Eocene 
is Podocrates [lltcnopH], scarcely to be distinguished from 
Wall-case Linuparns now living in Ja])anese waters. CaiUThins, also a 
Solenliofen genus, po,ssildy led to tlie Scyllarnhe, which are 
Table-case repi’eseiited in the English Gault and London Clay by 
ScjjllaHdia, and in the Chalk by Scylhmis. 
The true lobsters and crayfish are examjiles of the tribe 
Astacidea. These forms have pincer-claws on the first 
Table-case three pairs of legs, and the first ])air is very large. Already 
in the Lias we meet with Eryma, which is also found with 
Wall-case J'scudoasfncus in the Solenliofen .stone; these two, e.specially 
the latter, are very like the fre.sh water crayfish. In the 
Table-C^es Chalk, Enojjlocytia is fairly common and strikingly lobster- 
■ like. ])Ut HopJopariu, found in Cretaceous and Tertiarv 
rocks, is even more closely allied to the modern lobster 
(Homarus) and its near relation Nejjhrcps, of which the 
Norway lobster is a familiar example. 
Callianassa is a characteristic genus of the tribe Thalas- 
sinidea, Imrrowing forms, with a soft, loosely Imilt 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; Init this is only in one leg of tlie pair. From 
Table-case the Kimineridge Clay of England comes Callianassa isochcla, 
in which this flattened claw is not so disproportionately 
enlarged and is found in lioth 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. 
AVe come now to the Brachyura. Typical modern crabs 
differ from tlie decapods thus far described in the following 
characters among others : the abdomen is short and so 
bent up under tlie body that it is quite or almost invisible 
from above; the segment in front of the telson 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 
