52 DR. G. C. BOURNE ON THE RAN1NID.E : 
palfeontological evidence available, as far as it goes, supports this thesis. 
The Raniiiida3 are ancient forms among crabs, and when they make their 
first appearance have their characteristics fully developed. The earliest 
fossils of which I can find a sufficiently exact account are RanineUa Trigeri 
from the gres verts of Maine (France) and R. elongata from the cretaceous 
beds of the Sarthe. Both deposits belong to the Turonian division of the 
Cretaceous. In these early Raninidfe the carapace is of elongated oval 
shape, broadest in the anterior third j the "buccal frame" is so much 
elongated that it is nearly half the length of the body ; the thoracic sterna, 
wide between the first pair of legs, become narrowed between the second 
pair and are reduced to linear dimensions between the posterior pairs of 
pereiopods ; the four pairs of pereiopods are compressed and adapted for 
digging in sand (A. Milne Edwards 27). This is the description of a 
very typical Raninid of fossorial habit showing no greater affinity to the 
Prosoponidsb or to Protocarcinus (Palceinachus, -Woodvv.) than do existing 
members of the group. The presence of Ranina marestiana and Notopus 
Beyriclm in the Eocene show that modern genera of the Raninidfe were then 
differentiated and well established. Bittner's (3) excellent figure of the 
latter species might pass for a representation of the anterior half of the cara- 
pace of a modern Notojms. Perhaps the geological evidence proves no more 
than the antiquity of the Raninidse, but that antiquity affords support to 
the argument tliat they had an independent origin from the Astacura. 
If, then, they are not descended from a Protocarcinid-Prosoponid stock by 
way of the Dromiacea, a fortiori the Raninidse cannot be descended from 
the Dorippidse or Cyclodorippida?, which are themselves derived from the 
Dromiacea. From what lias preceded it is evident that they cannot be ; 
their primitive nervous sj'stem and endophragmal skeleton is sufficient 
evidence of that. On the same reasoning, the Dorippidse cannot be descended 
from the Raninidse, for it has been shown that their ancestry is altogether 
different. So one of the families, and that the most primitive, of the 
remainder of the Oxystomata is excluded from relationship with the 
Raninidse. What, then, of the two remaining Oxystome families, the 
Calappidre and the Leucosiidse. They are classified with the Raninidse 
because the majority of carcinologists have found it difficult to believe that 
the Oxystome "mouth frame" could have been acquired independently by 
different lines of descent. But since the Dorippidse are excluded from 
relationship with the Raninidfe this objection no longer has any force. But 
there is room for the opinion that the Calappidas and Leucosiidse are 
descended from the Raninidse, and I have already quoted (p. 26) de Haan's 
positive opinion that Lyreidus is an annectant form with the Leucosiidas. 
There are, of course, many points of difference between the Raninidse and 
the two above-named families. It would be an easy though a lengthy task 
