based on the Princijile of Cephalization. 



267 



They are the Stomapods of Latreille ; but this author, in his last 

 edition, made the group, in connection with the Schizopods, co- 

 ordinate with that of Decapods. Being co-ordinate with Brachy- 

 urans and Macrurans, the change of name is necessary. 



h. The Tetradecapods include two divisions precisely parallel 

 with the first two of the Decapods, the first literally hrachyural, 

 the second macrural. (See p. 97 of this volume.) The A^iiso- 

 pods of the writer, are degradational Isopods, just as the Ano- 

 murans are degradational Brachyurans. The Lemodipods (Ca- 

 prellids, &c.) are only degradational Amphipods, the structure of 

 the two being essentially the same in type. Hence, neither the 

 Lemodipods nor the Anisopods are an independent type corre- 

 sponding to a third division. 



The third subdivision probably is made up of Trilohites, 

 although these are generally regarded as Entomostracans. One 

 of the most prominent marks distinguishing Entomostracans from 

 Tetradecapods is the absence of a series of abdominal appendages. 

 It is highly improbable that the large abdominal (or caudal) plate 

 of an Asaphus, or the many-jointed abdomen of a Paradoxides, 

 Calymene, &c., should have been without foliaceous appendages 

 below ; and if these appendages were present, the species were 

 essentially Tetradecapods, although degradational in the excessive 

 number of body-segments. 



c. Entomostracans (or Colopods, as they are more appropriately 

 styled) embrace four orders. First, Carcinoids (as named by 

 Latreille) consisting of the Cyclops group (Copepods of Edwards), 

 whose species have a strong Macrural or shrimp-like habit ; to 

 which should be added the Caligoids, (Cormostomes of the writer, 

 Siphonostomes of others), since they are essentially identical in 

 type of structure with the Cyclopoids, as may be seen on compar- 

 ing Sapphirina of the latter with Caligus. — Second, Ostracoids (or 

 the Daphnia, Cypris, and Limnadia groups), which have, besides 

 a bivalve carapax more or less complete, a much more elliptic 

 abdomen than the Carcinoids, it being short, incurved, and with- 

 out a lamellar terminal joint or terminal appendages. — ^Third, 

 Limuloids, which have the abdomen still more elliptic, it being 

 reduced to a mere spine, or nearly obsolete, and which have the 

 • mouth-organs all perfect feet and the only locomotive organs. 

 (The joint across the carapax of the Limulus corresponds in 

 position to a suture or imperfect articulation in the carapax of 

 the Caligi, &c.) — Fourth, the Rotifers, a low Protozoic grade of 

 degradation, in which all members are wanting, and locomotion is 

 performed by cilia. The Phyllopods are distributed between the 

 first two divisions. 



The Rotifers are sometimes arranged under Worms. If they 

 are degradational species of a limitate type, they are Crustaceans ; 



