148 PROCEEDIXGS OF THE PALEOXTOLOGICAL SOCIETY 



brought forth a spirited discussion, the essential features of which are 

 reproduced below : 



RELATION OF THE HOLOCHOANITES AND THE 0RTH0CH0ANITE8 TO THE 

 PROTOCHOANITES AND THE SIGNIFICANCE OF THE BACTRITIDJE 



BY AMADEUS W. GRABATJ 



{Abstract) 



The suborder Protochoanites was proposed by Grabau and Shimer, in 1910, 

 for the reception of the Cambric genus Yolborthella, which is characterized, 

 among other features, by conical septa and a small siphuncle which is per- 

 fectly plain on the surface of the septa. It is considered ancestral, on the one 

 hand, to the Holochoanites, and on the other to the Orthochoanites. By a 

 crowding of the septa the endocones of the so-called siphuncle of the Holo- 

 choanites is produced, while a shallowing and separation of the septa produces 

 the septa of the Orthochoanites, The septa chambers of the Holochoanites 

 are a new feature. The endocones of the Holochoanites are considered the 

 homologues of the septa of the Orthochoanites. On this view, the "siphuncle'' 

 of the Holochoanites is the homologue of the entire Orthoceran shell, while the 

 endosiphuncle is the homologue of the Orthoceran siphuncle, and the endosi- 

 pholining, when present, the homologue of the Orthoceran shell proper. 



Bactrites is regarded as a lateral offshoot of the Orthochoanites, but not 

 ancestral to any Ammonitean cephalopods, which are direct derivatives from 

 Nautilian ancestors. The marginal siphuncle is a homoemorphic character and 

 has no ancestral significance. The possibility that Bactrites is ancestral to 

 the Belemnoidea is suggested by its similarity to the phragmocone of Atrac- 

 tites. 



Discussion 



The paper was discussed by Doctor Ulrich and Professors Schuchert, Clarke, 

 and Osborn. Professor Schuchert stated that he had, so far, failed to find 

 confirmation of the statement that the septa of Volborthella contains a median 

 opening or siphuncle. although he had examined a number of specimens in the 

 National Museum. A point also raised by Professors Schuchert and Clarke 

 and Doctor Ulrich was regarding the validity of the homologies between the 

 shell part of the Holochoanites and Orthochoanites suggested by the speaker. 

 In reply. Professor Grabau reminded his hearers that it was not his intention 

 to assert such homologies, but to reopen the question of the relationship of 

 these older forms. In the first place, it did not seem probable that such highly 

 specialized structures as the filling of the siphuncle of the Holochoanites should 

 appear in ancestral forms, from which by subsequent reduction and the dis- 

 appearance of these characters the less specialized siphuncle of Orthouras was 

 produced. Moreover, the ontogeny of the older Holochoanites, such as Pro- 

 terocameroceras, Xanno, etcetera, shows, according to the studies of Holm, 

 Clarke, Hyatt, Ruedemann, and others, that the siphuncle appeared before the 

 camerated part of the shell, Proterocameroceras, for example, having a very 

 long preseptal stage. It is true that the filling of this preseptal stage by endo- 

 cones is generally regarded as following the building of the first camer£e, but 



