Il8 ROCHESTER ACADEMY OF SCIENCE. [March 14^ 



into the Terebratulidce in which no calcified support for the coils was 

 produced, and that the forms in which the lamellre were continued 

 directl}' into the spiral coils without reversal of direction became the- 

 Spiriferidce, in which the spiral coil of the arms is supported by cal- 

 cified lamellse. 



From these facts I inferred that the two families at the stage of 

 their differentation, in the lower Silurian or earlier, were a continuous 

 series differentiating from a common stock. 



With this interpretation of the relations of the several forms to 

 each other, we conclude that the Pegmatobranchia were developed 

 from, or, strictly speaking, show closer affinities with the primitive 

 stock than with any particular family of the Eleutherobranchia, and 

 as a suborder find their natural place between the two divisions of the 

 ELleutherobranchia, for which I would propose the subordinal names, 

 Orihidacea, to include the Orthid?e, Strophomenidae and Productidce 

 and Pentameracea to include the families Pentameridje, Rhynchon- 

 ellidse and Porambonitidse. 



The following table will express the phylogenetic relations of the 

 several families suggested by the above considerations. 



Pentameracea 



Rhynchonellid?e. 



Pentameridte. 



(H. S. W.) ^ K •.• 1 



^ ' \ Porambonitidre. 



Pegmatobranchia 

 (Neumayr.) 



r Terebratulid?e. 



Thecididte. 

 \ Stringocephalidoe. 



I SpiriferidcX. 



I KoninchidcX. 



Orthidacea ( 



OrthidcT. 



(W ^ W "> "1 Strophomenid?e. 



^ ■ ■ M Productidae. 



The paper was illustrated by a model of the spiral " arms " and! 

 was discussed by the President and others. 



