14- Cumings — Morphogenesis of Platystrophia. 



hood of St. Petersburg. The beaks, as in most Spirifers 

 from the latter locality, are small, appressed and render it 

 difficult to view the double area" (p. 136). Of lynx he says, 

 " This variety differs from S. [Spirifer] biforatus only in the 



less number of plications in the sinus M. Eichwald says 



be found it in the drift near Grodno, with two plications in 

 the sinus, three on the fold and eleven on the sides" (p. 137).* 



So far as concerns the characters mentioned above as distinc- 

 tive of lynx and biforata, it must be admitted that none of 

 them are of any value. Platystrophia lynx has all the way 

 from one to seven plications in the sinus and may have from 

 six to twelve on either side ; and varies in shell index between 

 the limits of 1*0 and l'8.f 



It is altogether likely that the biforatus type does not occur in 

 American upper Ordovician faunas ; and the same may be true 

 of Eichwald's species, lynx. The latter certainly and Schlot- 

 heim's species in all probability, came from Russia. In regard to 

 biforatus, von Euch (loc. cit.) says, it " very likely came from 

 the north and not from France." With our present knowledge 

 of the species we may be sure it did not come from France, at 

 least, if it is an Ordovician type at all. It may very likely 

 have been obtained in the same manner as P. lynx from glacial 

 pebbles.^ 



I have before me specimens of the lynx, biforata, and dentata 

 types from the Ordovician of Russia. All of these show a 

 peculiarity that I have never seen in an American so-called 

 biforatus or lynx, from beds of equivalent age, namely, the 

 presence at the beaks of three plications on the fold and two in 

 the sinus. This peculiarity, as has been pointed out, invari- 

 ably characterizes Silurian forms both American and foreign. § 



Figures 6, 4& and 21e, are of these Russian types ; and show 

 the number and arrangement of the plications of the fold and 

 sinus. Fig. 21^, of the ventral valve of a specimen of P. 



* The shell index of biforatus given by deVerneuil is 1*5 : that of lynx 1*3. 



f Schuchert says (Bull. U. S. G. S. No. 87, 1897, p. 308), " Individuals of a 

 stratum .... are fairly constant in form, size, and plications, and it is this 

 limited constancy that has served in many of the following species [biforata, 

 lynx, laticosta, acutilirata, crassa]." Even this "limited constancy" can 

 scarcely be found in many localities, for I have seen several of the varieties 

 together in a single slab of limestone. 



Jit should be remembered that Schlotheim distinctly states that his " one 

 example" of Terebratulit.es biforatus came from Southern France. Either 

 he was mistaken or this type is a Mesozoic Spiriferina ! 



§ Mr. A. F. Foerste (Ball. Dennison University, i, 1885, p. 80) was the first 

 to call attention to the fact that Silurian forms have an odd number of pli- 

 cations on the fold and an even number in the sinus, while the reverse is 

 true of Ordovician forms. While this is not strictly true, it is true that the 

 Silurian forms have at the beak, without exception, three on the fold and two 

 in the sinus. 



