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 Denialhim, 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 Enchostnmida' 

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



The shells in the families HyolUhidiv and TentaculUidtv are 

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

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

 texture of the shells of Conularia or Enchosioma and Hyoltthes 

 or Tentnculiles as there is between the shells of Lingula or 

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

 for placing Conulariida; in an Order distinct from Hyolithidce 

 and Tentaculitidiv as there is for dividing the Brachiopoda into 

 the Orders Lyopomata and Arihropomata. 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, Hyoltthes and TentaculHes is 

 altogether different as well as the composition and texture. 

 (Jonularia are pyramidal Enchosioma round and curved toward the 

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

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

 lar. 



As a general rule a pahi'ontologist 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, anil 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 Coniilarida at present 

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

 mollusks and belong to the great Pala30zoic ages. 



CLASS CEPHALOPODA. 



ORDEll TETRABRANCHIATA. 



Family CIRTOCERATID.E. 



CYRTOCERAS DUNLEITHEN8I8, n. sp. 



Phiie III, Fif/. 11, lateral inew, showing a great part of the 

 chumher 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 



