868 THE PALEONTOLOGY OF MINNESOTA. 



[I'rotowarthia rectangularls. 



at least some of the forms of Protowarthia is delicately cancelled is not now consid- 

 ered of special consequence. A more significant fact is that while Protoivarthia is 

 almost or entirely restricted to the earlier periods of the Paleozoic, Warthia, if the 

 geological record is even approximately reliable and complete, did not make its 

 appearance till just before the close of that age. Here we have a difference in 

 geological distribution that can be accounted for in only two ways: either the 

 Permo-Carboniferous Warthia is distinct from Protowarthia and originated in some 

 nearly contemporaneous (say Carboniferous) type, or we must assume that the two 

 are the same and that the connecting species, which in that case must have existed 

 during the Upper Silurian, Devonian, Lower Carboniferous and Coal Measures, were 

 either destroyed or remain yet to be discovered. Considering the abundance of 

 other bellerophontids in these strata, the latter alternative is certainly very 

 improbable. 



On page 856 we express the opinion that Warthia (also Euphemus and Mogulia) 

 is a result of the decline and approaching extinction of the Bellerophontida;. As 

 stated there, such a return to primitive characters is quite in accordance with 

 theories that are rapidly entering the realm of facts. We would have been pleased 

 to discuss the questions involved at greater length, but the lack of space necessitates 

 a postponement to some perhaps more appropriate future opportunity. 



Compared with other bellerophontid genera Protowarthia is distinguished by 

 the absence of a slit-band and the width and size of the sinus in the outer lip; 

 Bellerophon has a distinct slit-band and centrally angular sinus and slit; in Owenella 

 there is an umbilicus, the sinus is much shallower and centrally subangular, and 

 the form of the shell more nearly globose; Bucanopsis has a slit-band, and so has 

 Bucania, coupled with a large umbilicus; finally, in Oxydiscus the whorls are 

 laterally compressed and sharply keeled and the shell broadly umbilicated. 



Respecting the species of Protowarthia, they are among the most characteristic 

 and abundant fossils of the Lower Silurian system. None are known in the Upper 

 Silurian and only a single Devonian species. The last, moreover, is doubtfully 

 referred to the genus. 



PROTOWAKTHIA RECTANGULARIS, n. sp. 



PLATE LXIFI, PIGS. 15-20. 



Shell of medium size, rather closely coiled, leaving only a small umbilicus in 

 the cast which, in the shell itself, is probably closed as in P. cancellata; outer volu- 

 tion sharply rounded dorsally, with a nearly flat or gently convex slope on each 

 side, then turning rather abruptly into the umbilicus; aperture transverse, subtri- 

 angular, about twice as wide as high, the width but little less than the bight of the 



