MACROURA. 501 



IT. ASTACIDEA. Carapax sutura dorsali transversa saepe notatus, 

 suturis longitudinalibus obsoletis, testa antero-laterali cum episto- 

 mate connata. Antennae externae squama basali sive nulla sive 

 parva instructoe. Pedes 6 postici directione fere consimiles ; antici 

 crassiores, sive didactyli sive monodactyli. [Branchiae penicil- 

 lataa.] 



III. CARIDEA. Carapax sutura nulla notatus, epistomate antice non 

 connatus. Antenna} externaa squama basali grandi instructae. Pedes 

 6 postici directione fere consimiles, Imi vel 2di crassiores et chelati, 

 3tii 4tis similes. [Branchiae foliosae.] 



IV. PENJEIDEA. Carapax sutura nulla notatus, epistomate antice non 

 connatus. Antenna? externas squama basali grandi instructaa. Pedes 

 Imi 2dique 3tiis non crassiores, 3tii saspius crassiores longiores et 

 chelati ; raro pedes toti debiles et tenues, 3tiis sive obsolete chelatis 

 sive omnino vergiformibus.. 



The Thalassinidea are related on one side with the Paguri, which 

 they approach in the carapax,. in the legs in part, and at times in the 

 form of the head and the base of the outer antennae (as in Gebia 

 especially) ; and, on the other side, they have affinities with the Squil- 

 lidae. The line of gradation which they occupy between the Ano- 

 rnoura and Anomobranchiates, is wholly separate from that occupied 

 by other Macroura. This section, therefore, is distinct in its range, 

 and cannot properly fall into the section Astacidea, where it is placed 

 by De Haan. 



The Astacidea, Caridea, and Penaeidea, viewed as a whole, consti- 

 tute together a second line, between the higher Decapods and the 

 Anomobranchiates, ranging towards the Mysidae. The first is the 

 highest group of the three, and. is partly Brachyural in its character- 

 istics. It is not, however, especially related in any points to the 

 Anomoura ; and we therefore view this line, not as a line of gradation 

 from the Anomoura down, but rather, that in which the Macroura 

 reach upward to their more exalted forms. The Astacidea are there- 

 fore the MACROURA SUPERIORA, while the Caridea are the MACROURA 

 TYPICA, and the Penceidea are the MACROURA INFERIORA. In the 

 same manner we might designate the Thalassinidea, descriptively, as 

 the MACROURA PAGURO-SQUILLIDICA. 



126 



