412 '^^lE GEOLOGIST. 



development of the arm itself, or of its connecting membrane ; and it is 

 therefore to be presumed that something similar did occur among the 

 species with spiral arms. 



The question relating to the classification of the species with spiral 

 supports is still a matter which will demand some further consideration ; 

 but it seems to me that the genera and sub-genera may be, for the 

 present at least, arranged into the following separate groups :— 



' Genus Spieifeea, Sow., type Sjj^ striata, Martin. 



? Sub-genus, Cyrtiai Dalmau, C. exporrecfa, Vfalil. 



5, Spiriferina, D'Orb., Sp. rostrata, Schloth. 

 „ Suessia, E, Deslong., S. costata, Desl. 

 „ Cyrtina, Dav., C. sej^tosa, Phillips. 



■Genus Athyris, M'Coy=^^j'in^6ra d'Orb. J. conccntrica, V. 

 Buch. 



Sub -genus, Merista, Suess, M. Ilerculea, Barrande. 

 „ „ Retzia King, R. Adrieni, De Yern. 

 „ „ Trematospira, Hall, T. perforata, Hall. 

 5, „ Nucleospirai Hall, N. ventricosa, Hall. 

 „ „ Uncites^'Def., U. GryphuSyD^f. 



a I g ( Genus Ateypa, Dalman=/^mterma, d'Orb., A. reticularis, 

 - / \ Linufieus. 



( Genus Koninckina, Suess, K. Leonliardi Weissman. 

 4 < ;, Anoplotheca, Sandberger, A. lamellcsa, Saudb. 

 ( „ Dayidsonia, Bouchard, Z>. Verneuilii, Boucli. 



Nos. 1, 2, and ^ have been grouped by myself and others into a single 

 family, Sjnriferidcd, but Mr. Woodward has excluded the third, which 

 he has added to the RhyncJionelUdce. 



A family, Davidsonidce, was proposed some years ago by Professor 

 King, in which some authors would comprise Anoplotheca and Koninckina. 



The characters which distinguish Spirifera, Atliyris, and Atrypa have 

 been so clearly defined, that there can exist no possible doubt as to the 

 propriety of maintaining all three as w^ell- established genera. 



The shells which compose Sowerby's remarkable and widely-spread 

 genus, Spieifeea, differ exceedingly in their external shape, some being 

 transverse, while others are elongated, rounded, smooth, angular, 

 variously ribbed or striated, with or without a mesial elevation in the 

 smaller valve and a sinus in the larger one, all possessing, however, a 

 straight hinge-lino, but very variable in length ; the larger valve is pro- 

 vided with a flat or concave, triangular or sub-parallel area, which varies 

 in height, width, and extent, according to the species ; the area is 



