GENUS SPIRIFERA, ETC. 251 



VI. ON THE GENERA SPIRIFERA, CYRTINA AND ALLIED GENERA. 



This paper will be deferred on account of the non-completion of a plate 

 illustrating the hinge-structure of Spirifera and allied genera, which will 

 be finished for the next report. In the mean time I will repeat here the 

 concluding remarks of the chapter on Spirifera from Vol. iv, Palsa- 

 ontology of New- York. 



"Some important considerations are suggested by the study of Spirifera 

 proBinatura, Spirifera alta^ and their associates. 



" The species which I have here designated as Spirifera prcBmatura 

 exhibits no external markings which enable one to say that it is distinct 

 from S. hirtus of the sandstones at Burlington, Iowa ; nor does it present 

 differences from S, pseudolincata which may not be reconciled with geo- 

 graphical influences, and with a habitat nearer to the shore line and 

 the essential absence of calcareous matter in the sediments deposited. Its 

 associates, however, are of different species from those in the western 

 locality ; but still among the more conspicuous of these is Spirifera alta^ 

 Productus lachrymosa var., and Chonetes muricata, which have a carbo- 

 niferous aspect ; and were it not for the presence of Spirifera disjuncta 

 and one or two others, the general aspect of the fauna might be termed 

 carboniferous. 



" If again we look at the characters of Spirifera alta^ an analogue or 

 representative of Spirifera cuspidata, we have many points of similarity 

 with one or more species in the rocks of the West and Southwest which 

 are usually referred to a higher position. The high area and the transverse 

 concave septum, which is not a true pseudo-deltidium, allies it with 

 Spirifera textvs^ in which we find similar features. In the S. alta there has 

 probably been an external convex pseudo-deltidium, and between this and 

 the septum closing the fissure has been a narrow space. This septum, 

 which is an extension of the dental lamellae, has been thickened or expanded 

 on the inner side, as shown by the casts of the ventral valve ; and in 

 several specimens there is a narrow semicylindrical depression extending 

 nearly to the beak of the valve. 



"In comparing this species with Spirifera textus^ we find similar condi- 

 tions, or more properly an extension or amplification of the same features. 

 In that species there is a convex arching pseudo-deltidium, though rarely 

 preserved in the specimens. Beneath this there is a concave septum, and 

 upon the inner face of this there is a tubular callosity; or, in other words, 

 the inner laminae of the septum become fistulous, and enclose a cylindrical 

 or subcylindrical space, which extends from the base of the septum to near 

 the apex of the valve. *^ But more usually the laminae appear to be sepa- 



* It is upon this feature, or one of similar character, in its full development, that I 

 understand Prof. Winchell proposes to found the Genus Sybingothyris. 



