64 AMMONITIDA. 
this reversal of terms as objectionable, inasmuch as their excep- 
tional use in the shells of tetrabranchiates. must give rise to 
great confusion. He uses also the word “ pile” for ribs, and 
‘“ oenicule ” for the knees of the ribs. 
A clear exposition of the reversed position of the animal of 
the tetrabranchiate, in relation to its shell, may be found ina 
paper by Prof. Owen, Zool. Proc., 955, 1878. 
Neumayr (1875) and Mojsisovics (1879, 1882) proposed sys- 
tematic arrangements of the Ammonitidz which agree in most 
of the main groups, but differ in details. The former dismisses 
Prof. Hyatt’s classification (limited to Liassic. species) with 
scant notice, his genera not being even enumerated, ‘‘ because 
they do not agree with natural groups.” I believe that both 
Hyatt and Neumayr would find it difficult to correlate their 
respective genera, The attempt has been made, however, by Dr. 
Paul Fischer in his excellent ‘ Manuel de Conchyliologie,” and 
if the result has not been satisfactory in all cases, it is at least 
far preferable to perplexing the student with three or more sets 
of generic names and diagnoses by presenting the several class- 
ifications in succession. I adopt Dr. Fischer’s conscientious 
arrangement for the present, and hope that it will, as soon as 
may be, give place to a better grouping. 
Siphonal neck of the septa directed backwards (Retrosiphonata). 
Goniatitee. 
Siphonal neck of the septa directed forwards (Prosiphonata). 
No Aptychus, or corneous Anaptychus of one plate (Anap- 
tychidea . 
First saddle of the suture broad (Latisellata). Arcestie, 
Tropite, Ceratitee, Clydonite. 
First saddle narrow (Angustisellata). Pinacocerz, Amal- 
thee, Ammonitz, Lytocere, Phyllocere. 
Aptychus calcareous, double, or of two valves soldered to-, 
gether (Aptychidea). Harpocerz, Stephanocere. 
As Dr. Fischer regards the Ammonitidze as an order, he has 
given the family termination to the above names: they will 
here be considered as group-names for assemblages of genera of 
the family Ammonitide. The position and appearance of the 
lobes and ules of the septal sutures are represented and ex- 
plained, i, 22,28; xxxin, 31 > xXx xi, 4s xxxiy, O1 O2t xe (2. 
Goniatite. 
Shell nautiloid; siphonal neck of the septa directed back- 
wards. Siphon excentric. First whorls of the spire sometimes 
contiguous and covered as in Ammonites, sometimes not in con- 
tact, as in those of Spirula. 
