THALASSOCERATIDAE Hyatt 



Prothalassoceras nov. gen. 

 Type, Prothalassoceras Welleri Bose 



Gemmellaro's genus Thalassoceras shows a very simple suture line 

 which consists of an extremely wide siphonal lobe divided in two 

 branches by a high median saddle ; two lateral lobes, strongly digitate 

 or dentated; and two saddles broad at the base, dentated on the flanks, 

 rounded at the top, and with simple outline. 



Among the species described by Gemmellaro is Th. varicosuw} 

 which shows a peculiar but simple suture at a diameter of 7 mm. It is 

 so different from the mature suture of the other species that it probably 

 has to be considered as a stage in the development of Thalassoceras. 



Karpinsky^ has described from the Russian Artinsk a Thalassoceras 

 Gemmellaroi which shows a similar, although perhaps still a little sim- 

 pler, suture. The specimen has a diameter of 11 mm. The suture is 

 made visible at the front end of the last whorl; at the back end it is 

 still somewhat simpler. 



As Karpinsky's specimens are still relatively small, the largest one 

 having a diameter of 11 mm. and the smaller one of 6 mm., one might 

 be inclined to take that suture also only for a stage in the development 

 of Thalassoceras, but we find in our Texas Permo-carboniferous a 

 species which is certainly adult, having a diameter of more than 

 47 mm., and which shows in general the same suture as Th. Gemmel- 

 laroi and as the immature Th. varicosum. As this form is certainly 

 older than the Sicilian species, we have to consider it as a new genus 

 and as an antecessor of Thalassoceras; its suture line being passed 

 through by Thalassoceras in its first stages. Until now only one 

 specimen has been found, so that it was impossible to prepare the 

 sutures of the smaller whorls. 



Our new genus (pi. V, fig. 14-18) shows the following character: 

 Shell discoidal, extremely involute, with compressed flanks and rounded 



'Gemmellaro, Calc. c. Fusulina, p. 72, pi. 5, fig. 20-22; pi. 7, fig. 33, 34. 

 ''Karpinsky, Amm. d. Artinsk-Stufe, p. 80, pi. 4, fig. 3a-d. 



