564 Revieics — G. H. Girty — Guadalupian Faumt. 



being applied to the plicated shells. Another group of Orthotetinne is 

 composed of species in which the ventral valve is provided " with two 

 more or less parallel dental plates without median septum. The 

 plates are prolonged to meet the anterior or convex wall of the shell". 

 When the dental plates are long and parallel and the shells non- 

 plicated, we have the genus OrthotJietina. Plicated forms are placed 

 under Meehella. Shells with short and diverging dental plates are 

 without a distinctive designation. 



The question miglit naturally be raised as to the value of septal 

 development, external plications, areas, etc., in generic classification. 

 It is probable that some workers, with Jakowlew, would minimize in 

 any detailed subdivision the value of areas, or, with Scupin in " Die 

 Spiriferen Deutschlands", the importance of septal division. Jaekel 

 in his paper on phylogenetic development considers external characters 

 to be only valuable for specific distinction. Presence or absence of 

 external plications would, on this view, be insufficient for generic 

 definition. Girty expresses a doubt as to whether all the features 

 used for distinction are of equal taxonomic value, and applies the 

 doubt particularly to the generic separation of Orthotetes and Geyerella, 

 Orthothetina and Meehella. He would consider as appropriate for 

 recognition 8treptorhy}icJms, Schuchertella^ Derbya, Orthotetes, and 

 Orthothetina, but uses Meehella and Geyerella -as genera in the mono- 

 graph under consideration. 



In discussing the cardinal process of Streptorhynchus halUanum as 

 figured by Hall and Clarke, Girty suggests the probability that the 

 cardinal process, like other areas of muscular attachment, "is sub- 

 jected in old age to excessive shell secretion, not only increasing its 

 size, but by strengthening its muscular features, also modifying its 

 shape, so that the process varies much in both particulars, owing to 

 difference in age." A somewhat similar opinion has been expressed 

 by other palaeontologists, e.g. Drevermann in his treatment of the 

 Spirifer casts of the Devonian. Schellwien considered that the 

 median septum was a development from the dental plates, a view 

 which the author of the present work is inclined to dispute. He 

 considers the median septum and dental plates to be independent 

 structures, "though all converge and unite at the apex of the ventral 

 valves, where they often merge in a solid shelly mass." It is 

 interesting in the same connexion to note Jakowlew's opinion that 

 a plate developed adjacent to the spondylium in Cyrtina carhonaria 

 corresponds to a pseudodeltidium. 



Martinia is based on the peculiaritj" of external configuration 

 together with the absence of septal plates. The outer layer, when 

 preserved, is assumed to be punctate. Reticularia is regarded as 

 possessing well-developed dental plates and median septum. Some 

 of the recent descriptions of Reticularia by Vaughan, Sibly, and 

 others contain no reference to the presence of a median septum. 

 Lee, therefore, makes the interesting suggestion, in his recent paper 

 on the Nova Zembla Carboniferous Fauna, that there may be 

 Reticularia - like forms possessing dental plates without median 

 septum. Shells so characterized would probably be entitled to specific 

 if not sub-generic value. McCoy's original diagnosis of Reticularia 



