284 



CRUSTACEA. 



laticaudes," in which the abdomen arises with a broad base as the direct pro- 

 longation of the thorax. Richters, on the other hand, has conjectnrally 

 referred the Brevicaudes to Ibacus and Paribacus. Fossil Phyllosoma have 

 been recognised in the Solenhofen slates. 



F. Thalassinidea. 



The larvae of the Thalassinidea (Gebia, Calocaris, Callianassa, 

 Calliaxis), known to us from the treatises of G. 0. Sars (No. 149) 

 and Claus (Nos. 6, 7, and 8), are allied to the Caridid larvae by 

 the shape of the body, the possession of a long rostral spine, and 



the peculiar armature of the; 

 abdomen (wanting in Gebia) ; 

 this latter consists of a long 

 dorsal spine on the second 

 and shorter spines on the 

 three following abdominal 

 segments. Their metamor- 

 phosis is, however, of special 

 interest on account of the 

 complete transition which 

 they exhibit between the 

 manner of development of 

 the Caridids and that of the 

 Anomura and Brachyura. 



The youngest larval stage 

 of Gebia (Fig. 132 A) is a 

 Zoaea wdiich is distinguished 

 from the Zoaeae of other 

 Macrura chiefly by the fact 

 that only the two anterior 

 maxillipedes (mf, mf") func- 

 tion as biramose swimming 

 limbs, while the third maxil- 

 lipedes, as well as the four 

 following ambulatory limbs, 

 are found as rudiments devoid of setae, the four anterior pairs being 

 biramose, while the most posterior pair is still simple. The fifth 

 pair of ambulatory limbs, as well as the pleopoda, are still altogether 

 wanting. The telson, which is not yet marked off from the sixth 

 abdominal segment, is a spade-shaped plate somewhat indented ai 

 itfl posterior edge and beset with setae. The paired eyes, which 

 till immovable, recall those of the Anomuran larva, in the 



I'm;. 132.— Two larval stages of Gebia littoralis (after 

 G. O. Sars). A, Zoaea stage (dorsal view). /-', 

 Mijs'is stage (side view), a', first antenna ; «", 

 second antenna; cfl-cfi, rudiments of the live 

 posterior abdominal appendages; mf, mf", mf", 

 the three maxillipedes; pl-p^, the five ambula- 

 tory limhs ; or, Nanplins eye. 



