70 University of Texas Bulletin 



tive lobe is very little pronounced, while in geologically younger 

 species it reaches a considerable width and depth, and seems to re- 

 present a lateral lobe; (2) that in geologically older species the number 

 of rudimentary adventive lobes is smaller than in geologically younger 

 species; (3) that in geologically older species all the lateral lobes with 

 exception of the first one are asymmetrically bifid in such a manner 

 that the finger nearer to the umbilicus is longer and stronger than the 

 other : geologically younger species begin to show symmetry and it 

 even appears as if in the geologically youngest species the reversed 

 arrangement is taking place. 



Noetling bases this hypothesis on the supposition that the Sicilian 

 Sosio beds are older than the Russian Artinsk, and that this horizon 

 for its part is older than the Productus limestone of the Salt Range 

 of India. But this succession is by no means universally recognized. 

 On the contrary, by far the majority of the authors considers the Rus- 

 sian Artinsk to be somewhat older than the Sicilian Sosio beds, and 

 while the upper and part of the middle Productus limestone is generally 

 considered as being younger than the Sosio limestone, all the lower 

 Productus limestone is considered as being older than those beds. 



Noetling says that if it should be proven that his supposition with 

 respect to the relative age of the horizons mentioned is wrong, all 

 his conclusions would be untenable, but it would also be shown that the 

 ontogenetic development of the suture cannot be used for any kind 

 of conclusions with respect to geological age. 



I do not think that in this case the consequences would be so terrible 

 as Noetling paints them. I would rather suppose that this author 

 overestimates the value of an adventive lobe and does not always take 

 into account the influence of size on the development of the suture. 



Most of the Sicilian species are rather small, but we know nothing 

 about the real size of the complete specimen because, apparently, none 

 with a body chamber has been found. At least, Gemmellaro, who al- 

 ways pays great attention to the length of the body chamber, does not 

 even mention its size in his description of the different Mcdlicottia. 

 The only species from the Artinsk is not very large, and a comparison 

 with that from the Productus limestone is rather difficult. 



In his first paragraph Noetling asserts that the adventive lobe is 

 much less conspicuous in the older forms than in the younger ones. 



