vi 
INTRODUCTION. 
(6) Metachoanites, or those with the necks of the septa turned back- 
wards, and thus forming a complete shelly tube, e.g. Endoceras, 
Trocholites. 2. Ellipochoanoida, species with short necks and the 
siphuncular tube completed by an “ intervening connective wall of 
distinct structure from the septal funnels.” The Ellipochoanoida 
are subdivided into the “ true Microchoanites, which embrace the 
Actinoceratidce, and most of the true Xautiloids, including Nautilus ; 
and the Macrochoanites, which may be said to include Bactrites and 
such straight forms as are transitional to Ammonoidea and all the 
Nautilinidse, and also the Clymeninse, which havesimilar long funnels.” 
Another term, Cloiochoanites, is employed by Hyatt to include “ the 
transitional forms of the Goniatitince, which have the short type, 
or partly cloiochoanitic funnel elevated upon a median siphonal 
saddle ...” He adds : — “ An important factor in this classification 
is the dorsal suture, and we find that the position of a genus may often 
be determined in any given series by the peculiarities of this part ; 
whether it is present or absent, and w^hether it has, or has not, a 
small annular lobe, or ‘ spindle lobe,’ or a small saddle in the 
median line of the dorsum.” 
Hyatt next discusses the embryonic relations of the structure of 
the septa and of the siphuncle, and mentions the diflPerence between 
the Nautiloids and the Ammonites exemplified in these structures, 
the one commencing with a globular initial chamber (protoconch of 
Owen), the other with a conical initial chamber and a cicatrix. He 
remarks that generally among the Palaeozoic Cephalopod types much 
greater differences exist, in regard to the septa, the position of the 
siphuncle, and so on, than among the Mesozoic forms, thus indica- 
ting that the evolution of forms was quicker in the Palaeozoic epoch 
than at subsequent periods, and from these circumstances he concludes 
that “ types are evolved more quickly and exhibit greater structural 
differences between genetic groups of the same stock, while near the 
point of origin, than they do subsequently.” It must not be for- 
gotten, however, that the Palaeozoic epoch was of much longer 
duration than the Neozoic. In the smaller divisions (Eamilies and 
Genera) of Hyatt’s scheme of classification an important place is 
assigned to the characters of the sutures for distinguishing the 
different groups. In some groups, however (notably the Ortho- 
ceratidae), the less stable characters presented by the ornamentation 
of the shell are for a like purpose employed. 
^ hile there can be no question as to the value of Professor 
Hyatt s work, and the thoroughness of research which he has brought 
