SUBCLASS II 



EÜCßUSTACEA— EUCARIDA 



765 



The Dromiacea take the lowest place among the tribes composing this section, 

 differing from the more specialised Brachyura in retainiiig iiiany primitive characters. 

 Thus, the last somite of the abdomen often retains vestiges of uropods, the first 

 abdominal somite of the female has a pair of appendages, the fossettes for the reception 

 of the antennules are less cleaiiy defined, and the gills are more numeroiis. 



Among the Recent Dromiacea, again, the family Homolodromiidae is the most 

 primitive, its members, which inhabit the deep sea, presenting many features which 



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Fig. 1484. 



A, Prosopon marginatum v. Meyer. Upper Jura (e); Oerlinger Valley, 

 near Ulm. s/g. B, P. personatum. Upper Jura (y) ; Weissingen, Würtem- 

 berg. Rostrum enlarged. C, P. amleatum v. Meyer. Same locality as A. 

 D, P, pnstulaium Quenst. Same locality as A. 



Fig. 1485. 



Dromiopsis rugosa 

 (Schloth.). Uppermost Cre- 

 taceous ; Faxoe, Denmark, 



l^l ' 



link them with the Lobsters of the tribe Nephropsidea. It is therefore of special 

 interest to find, as Bouvier has shown, that the earliest fossil Brachyura, forming the 

 extinct family Prosoponidae, are allied, by the form of the carapace and the disposition 

 of the grooves upon it, to the existing Homolodromiidae. In the majority of cases 

 the carapace alone is preserved, but portions of the abdomen and limbs are known in 

 Protocarcinus (Palaeinachus) Woodward, from the Forest Marble (Bathonian) of 

 England. The genus Prosopon von Meyer (Fig. 1484) is of even earlier date, 

 appearing in the Bajocian and persisting to the Neocomian. Later forms approach 

 more specialised Recent types, such as Homolopsis Bell from the Gault, leading towards 

 the Homolidae; and Dromiopsis Reuss (Fig. 1485), leading towards the Dromiidae. 

 The Tertiary Dromilites Milne Edwards, is scarcely different from the Recent Dromia. 

 The tribe Oxystomata is characterised by the form of the mouth-frame, which is 

 triangulär and produced to the front of the head between the eyes. The earliest 

 example of the tribe is Mithracites Gould, 

 from the Lower Greensand. Palaeocorystes 

 Bell (Fig. 1486), ranges from the Gault 

 to the Eocene. Eucorystes and Necrocar- 

 cinus Bell (Fig. 1487), are found in the 

 Gault and Upper Greensand. The precise 

 relations of these to modern families are 

 doubtful. The Recent Calappa and 

 Matuta Fabr., however, are known from yw. i486. 



Eocene and later deposits. Palaeocorystes stokesi 



The remarkable family Raninidae, Jf^eeisand ; ^Cam^ 

 distinguished by the unusual form of the bridge, England, 

 chelae and by the elongate carapace, 



which is broader in front than behind, is known as early as the Cenomanian chalk, 

 and its representatives are not rare in the Tertiary. Raniella and Raninoides 

 Milne Edwards, are Cretaceous genera. Of the few Recent genera, Ranina Lamarck 

 (Fig. 1488) is known from the Eocene. 



The tribe Brachygnatha, in which the mouth-frame is quadrate, includes the great 

 majority of the Brachyura. It is divided into two subtribes, the Oxyrhyncha and. 

 Brachyrhyncha. 



Fio. 1487. 



Necrocarcinus' tricarinatus 

 Bell. Greensand ; Cam- 

 bridge, England (after Bell). 



