30 



pose the family name Enchostomidce, but the family name as at 

 present understood, will take the same definition that the genus 

 has. We have seen fragments of a long, arching, round shell, 

 somewhat, in form, like a Dentalium, in limestone, belonging to 

 the Keokuk Group, but having the shell texture of this genus, 

 that may be generically distinct and if so the family Enchostomidce 

 may be defined and limited so as to include two genera. 



The shells in the families Hyolithidce and Tentaculitidce are 

 thick and composed of layers that may sometimes be horny, but 

 they are never phosphatic. There is as much difference in the 

 texture of the shells of Conularia or Enchostoma and Hyolithes 

 or Teniaculites as there is between the shells of Lingula or 

 Discina and Orthis or Spirifera. And there is as much reason 

 for placing Conulariidce in an Order distinct from Hyolithidce 

 aDd Tentaculitidce as there is for dividing the Brachiopoda into 

 the Orders Lyopomata and Arthropomata. The fundamental dif- 

 ference in the composition and texture of the shells is the basis 

 of the separation into Orders. The general form of the shells in 

 the genera Conularia, Enchosioma, Hyolithes and Tentaculites is 

 altogether different as well as the composition and texture. 

 Conularia are pyramidal Enchostoma round and curved toward the 

 apex and ovate toward the mouth, Hyolithes short, flattened on 

 one side and straight, and Tentaculites straight, round and annu- 

 lar. 



As a general rule a palaeontologist is able to classify the fossils 

 with reference to some known living organism. He finds a trace 

 or path from the unknown animal to the known, and reasons 

 forward from remote ages to the present, and he finds here and there 

 a fauna that characterizes a geological age and enables him to 

 determine it at distant localities, but the Conularida at present 

 are to be classified with the unknown, save that they are evidently 

 mollusks and belong to the great Palaeozoic ages. 



CLASS CEPHALOPODA. 

 ORDER TETRABRANCHIATA. 

 Family CYRTOCERATID^. 



CYRTOCERAS DUNLEITHENSIS, n. sp. 



Plate III, Fig. 11, lateral view, showing a great part of the 

 chamber of habitation; Fig. 12, transverse section. 



Shell medium size, strongly curved and regularly enlarging 

 from the apex to the mouth. The siphuncle is on the ventral 

 side or outer margin of the curve and produces an expansion of 



