612 NEW YORK STATE MUSEUM 



the cephalopod body, the following obstacles must first be 

 cleared away: 1) They are usually completely dissociated from 

 the cephalopod shells. 2) Some forms of Discinocaris and Pelto- 

 caris of the early Siluric are virtually indistinguishable save 

 for outline and size from Spathiocaris and Cardiocaris of the 

 Devonic. The former appeared at a time long antecedent to 

 the ammonoids. We know that one of those early species was 

 brachiopodous, the others are not goniatitine; the later forms 

 can hardly match our conception of brachiopod structure. Ob- 

 jects of iso similar a character would a priori be of similar nature, 

 an argument which, if carried to a logical conclusion, would 

 wreck the inferred goniatitine character of the Devonic genera'. 

 In meeting these obstacles it is to be borne in mind that no sin- 

 gle specimen of any of the genera Discinocaris, Pholadocaris, 

 Spathiocaris, Cardiocaris has been proved crustacean. The seg- 

 ments and spines referred to these may or may not have any 

 relation to the shields themselves. 



There is a series of these shields which is unlike those 

 specially mentioned above, in having a triangular cleft at both 

 extremities, that behind not reaching to the apex or growth 

 center of the surface, but often broader than the anterior cleft. 

 These are wholly Devonic objects and have been termed 

 by the writer Dipterocaris. American specimens have been 

 found not so much in the bituminous layers of the upper 

 Devonic as in the flags and sands, and certain specimens have 

 clearly indicated that in uncompressed condition the contour 

 was distinctly sloping from the bridge between the two lateral 

 wings of the shield. Among these specimens there is no room 

 for any suspicion that they have brachiopodous affinities. 

 Regarded as Crustacea, that is Phyllocarida, at the time of the 

 description of the genus, the crustacean similarities are indeed 

 more strongly marked than in the Spathiocaris class of 

 shields, a feature specially brought out on comparison between 

 such a Dipterocaris and the carapace of a phyllocarid like 

 Rhinocaris or Mesothyra; but on the other hand the gen- 

 eral form, structure and surface characters of all these 



