8 BRITISH PALAEOZOIC PHYLLOCARIDA. 



of the Carboniferous epoch, that any decision affecting its zoological position 

 cannot be a matter of indifference to the pateontologist. 



But after studying its larval development and adult structural modifications, 

 we arrive at the fact that Nehalia is a more generalised type than is ordinarily to 

 be found at the present day, " combining Copepod, Phyllopod, and Decapod-like 

 features, with other more fundamental characters of its own" (Packard), which 

 preclude us from regarding it as a true Malacostracan, and, although ancestrally 

 related to that order, it nevertheless does not attain, in our opinion, to the Mala- 

 costracan grade of development.' The group should therefore be arranged in a dis- 

 tinct order (the Phyllocaeida) between the Entomosteaca and the Malacosteaoa, as 

 suggested by Claus. But if it is undesirable to have such an outstanding group, 

 then we contend that the balance turns in favour of retaining it in the former 

 division, if not in the order Phyllopoda as heretofore. 



Thus we conclude — 



1. Some of the supposed "Phyllopod shields" from the Bifel and elsewhere 

 are probably Aptychi of Goniatites. 



2. That for others of the Palfeozoic Phyllopods, described in our Reports of 

 1883-84 (British Association), this explanation is inadmissible. 



3. That those which cannot be referred to Aptychi are still, in all probability, 

 Phyllopods (Phyllocarids). 



4. That the Nehalia-Vike forms, now placed in the order Phyllocaeida, are 

 certainly not Decapods. And even if they may not with propriety be retained any 

 longer in the old order Phyllopoda (of which we are by no means sure), yet they 

 may more correctly be placed beside them in the Entomosteaca than in the Mala- 

 COSTEACA, seeing they have not actually attained to the grade of the latter, but only 

 approached to its larval development ; whilst with the former the adult Nebalia has 

 many very strong points of affinity. 



Ceratiocaeid^. — Dr. Packard's observations on the structure of the Phyllopods, 

 and his studies of the comparative anatomy of living and fossil forms, supply the 

 palseontologist with sound reasoning in referring the Phyllocarida to the Nebaliad 

 type as a centre for a great group of obscure fossil forms, and as a starting-point 

 for the Decapoda. We have referred to his views in some detail in the foregoing 

 pages, and it is our present intention to treat of the group typified by Ceeatiocaeis, 

 which has more than others a strict alliance to the recent Nehalia. 



1 Dr. Packard writes " There is little to indicate that the Schizopods (Mysis, &c.) have descended 

 from a JVeSoZm-like form, but rather from some accelerated zoea form; while the Phyllocarida have 

 had no Decapod blood in them, so to say, but have descended by a separate line from Copepod-like 

 ancestors, and culminated, and even began to disappear, before any Malacostraca, at least in any 

 numbers, appeared " (' American Naturalist,' 1882, vol. xvi, p. 873). In his " Eeport on the Schizopoda 

 collected by the Challenger," 1885, and " On the Phyllocarida," 1887, Prof. G. O. Sars treats oi Nebalia 

 as being not a true Phyllopod, but a " Copepodiform Branchiopod ;" p. 5. 



