782 PROF. T. H. HUXLEY ON THE CLASSIFICATION [June 4, 



If the branchial filaments of Axius were shortened and widened, 

 the structure of the branchiae would approach that which obtains in 

 Gebia and Callianassa, which are truly phyllobranchiate. But in 

 other respects there is a wide interval between these genera, on the 

 one hand, and Axius and Thalassina, which are ordinarily associated 

 with them among the Thalassinidae, on the other hand; for the 

 podobranchiae have entirely disappeared on the six hinder thoracic 

 limbs, and even on the first or second maxillipede they are repre- 

 sented only by rudimentary epipodites. 



There are no pleurobranchiae; and the total number of gills is re- 

 duced to five pairs of arthrobranchiae on each side. 



The Branchial formula of Gebia and Callianassa. 

 Somites Podo . Arthrobranehi*. pieupo . 



and their branchi . v ,_ j-; ^— p. branchiae. 



appendages. Anterior. .Posterior. 



VII = 



VIII = 



IX 1 1 = 2 



X 1 1 = 2 



XI 1 1 = 2 



XII 1 1 = 2 



XIII 1 1 = 2 



XIV = 



+ 5 + 5 + 0= 10 



In the almost complete abortion of the podobranchise, and in the 

 presence of ten arthrobranchiae attached in pairs to the middle tho- 

 racic somites, Gebia and Callianassa agree with Porcellana, Gala- 

 thea, Lithodes, Pagurus, and Remipes. But in Gulathea and 

 Porcellana the four hindermost pleurobranchiae are present, making 

 fourteen gills on each side ; in Lithodes and Pagurus the penul- 

 timate pleurobranchia exists, making eleven ; in Remipes there is no 

 pleurobranchia, and only nine arthrobranchiae, viz. one on the ninth 

 and two for each of the four following somites, are present. 



In this group, which nearly corresponds with the Anomala of De 

 Haan, and which I propose to term the " Anomomorpha," there is 

 every degree of modification — from such typically Macrurous forms 

 as Gebia and Galathea to such pseudo-carcinoids as Lithodes and 

 Porcellana. It is interesting to remark, however, that, while in 

 Thenus and Ibacus the process of modification has chiefly affected 

 the head, in the Anomomorpha the characteristic changes are more 

 marked in the abdomen. In none of the latter are the basal joints 

 of the antennae fixed, nor are distinct orbits formed. 



It is easy to understand the possibility of the derivation of the 

 Anomomorpha from some form allied to Axius and Thalassina (but 

 with four pleurobranchiae) by the further reduction, and final almost 

 complete disappearance, of the podobranchise, while the biserial 

 filaments of the other gills flattened out and became lamellar. 



The Prawns and Shrimps ( " Salicoques " of Milne-Edwards, Carides 



