Revieius — The BracJtiopod genus PIafysiro2'>]i'ia. 89 



slight differences between it and Terehratula lynx Eicliwald. If the 

 characters he reported are again rendered inadequate by the advance 

 of knowledge, then surely the obvious course is to re-examine the 

 holotype. Has this been attempted ? If the holotype has dis- 

 appeared, then in any attempt to fix the species regard should be 

 paid to Schlotheim's statement that the unique specimen came 

 " aus dem slidlichen Frankreich ", though Von Buch thought it 

 more probably came from the North (i.e. the Baltic region). The 

 species has always been regarded as a close ally of P. lynx, and it 

 ought to be possible to determine that species with precision. If, 

 however, the attempt to elucidate P. biforata be given up, then the 

 alternative course is to select as genotype one of the other species 

 mentioned by King (1850) when he established the genus, namely 

 Sioirifer tcheffkini De Vern., Poramhonites dentata and costata 

 Pander, and Spirifer terebratuUformis M'Coy. None of these is 

 mentioned by Miss McEwan, who prefers to select a species intro- 

 duced twenty-three years later and found many thousand miles 

 from the type-locality. The fact that Miss McEwan lives in Illinois, 

 or even the fact that American intercourse with Germany has been 

 interrupted for a few years, cannot justify this calm setting aside 

 of all early descriptions and material. 



So far as North American species are concerned, Miss McEwan's 

 paper continues the line of research initiated by E. R. Cumings in 

 1903, when on the basis of characters in the young shell he separated 

 the species into Uniplicate, Biplicate, and Triplicate. In the 

 Uniplicate series the single plication on the sinus and the two on the 

 fold continue through life. The Biplicate series starts with a bifur- 

 cation of the plication on the sinus and an intercalated median 

 plication on the fold. According as further bifurcations and inter- 

 calations do or do not take place, the series is divided into four 

 sub-groups. In the Triplicate series, to which most North 

 American species belong, the single plication of the sinus persists, 

 but is soon flanked by a plication on each side ; the two 

 plications of the fold bifurcate. This series is divided into 

 three sub-groups. In two of them called Low Fold and 

 High Fold, the hinge-line is relatively long and the brephic 

 and early neanic stages are similar ; in the former sub-group 

 the low rounded fold persists, and the plications of both fold 

 and sinus remain of nearly the same strength ; in the latter sub- 

 group the fold becomes high and compressed in the late neanic 

 stage, and assumes an angular appearance owing to the obsolescence 

 of the lateral plications. The third sub-group does not as yet seem 

 to be very clearly defined, but is constituted for large heavy forms 

 generally similar to the P. ponderosa of Foerste, and probably 

 arising at various periods as gerontic forms of Low Fold species. 



In the groups as thus defined by brephic and neanic characters 

 Miss McEwan recognizes many cases of parallelism and convergence, 

 and these seem to her to show " that the ancestral species had certain 



