THE PALEONTOLOGY OF MINNESOTA. 



[Bellerophontlldee. 



Permo-Carboniferous of India, W. polita, W. brevisinunta and W . lata. To these he 

 adds three Australian species, Bell, undulatus Dan., Bell, strictus Dan., and Bell, 

 micromphalus Morr. 



MOGULIA, Waagen, (Pal. Indica, ser. 13, pt. 2, pp. 181, 156; 1880.) General 

 appearance of shell as in Bellerophon, from which it differs in having no slit nor slit- 

 band, and only a shallow angular emargination in the outer lip. Surface markings 

 consisting of lines of growth only. These are broad and strong and cross over the 

 dorsum without further interruption than is occasioned by the sharp central bend. 

 Only known species, M. regularis Waagen, Permo-Carboniferous of India. 



This and the two preceding genera, Euphemus and Warthia, are of unusual 

 interest because we believe they show that in the decline of the family it actually 

 retraced its steps by the adoption of primitive characteristics. In other words we 

 regard them as atavistic types in which the progressive development of the indi- 

 vidual was arrested in the embryo, and in which, because of the failure to develop 

 the adult features of their immediate ancestors, certain characters that under 

 previous conditions were larval only became permanent. In the Devonian and 

 Carboniferous Bellerophontiidce the suborder obtained the hight of its development, 

 and this was not reached until after the extinction of all the other families. The 

 decline, which obviously was very rapid, took place during the time immediately 

 preceding the close of the Paleozoic age. Facts like these permit us to assume that 

 the three genera under consideration are retrograde descendants of Carboniferous 

 BellerophontiidcK and not remnants of types that flourished only in Cambrian and 

 Lower Silurian times. Besides, this idea is entirely harmonious with laws that 

 have been shown to operate in other branches of zoology, and according to which 

 the earliest and latest representatives of a group of organisms may be more like 

 each other than either is like intervening stages in the rise, acme and decline of the 

 line of evolution to which they belong. 



Mogulia, in the absence of a slit-band, the shape of the outer lip, the form of the 

 aperture, and even in the strength and course of the lines of growth on the dorsum, 

 compares closely only with Owenella, that most ancient of all the Bellerophontacea. 

 Warthia, excepting that it has no spiral surface lines, nor those grano-lineate exten- 

 sions of the inner lip, is precisely like that important group of Lower Silurian 

 shells which we have called Protowarthia. Euphemus, again, in its broad and ridge- 

 bordered slit-band, in the shape of the aperture, indeed in the form and characters 

 of the whole shell, recalls the Lower Silurian genus Tetmnota probably more than 

 either Owenella and Protowarthia. But in the spiral columellar folds which spread 

 over the umbilical regions and a large part of the dorsum of the last volution, we 



