1883.] 269 [Hyatt. 



shoulders smooth but gibbous, the type has this part of the whorls 

 elevated into a ridge. The forms are evidently transitions from 

 the genus Plectoceras to Mojsvaroceras. Type, Meta. (Discus) 

 Sangamonense, M. et W., Geol. Surv. 111., Vol. 2, pi. 29. Meta. 

 (Lit.) occidentale, sp. Hall from Trenton of 111. Am. Mus. N. Y., 

 is the transitional type from Plectoceras to Metacoceras. 



Tainoceras 1 , nobis, includes Carboniferous and Triassic forms 

 with discoidal whorls, section quadrate and closely resembling 

 Mojsvaroceras in every way, having also two lateral' rows of tuber- 

 cles, but possessing on the abdomen two additional rows of tuber- 

 cles in the later stages of growth, and adults. The siphon is 

 above the centre. The sutures have ventral, lateral, and dorsal 

 lobes but no annular lobes. The young of the type species has 

 not the abdominal tubercles, and is similar in all characteristics 

 to the Mojsvar. (Naut.) Wulfeni. sp. Mojsis. Das. Geb. Hallst. 

 Abhand. Geol. Reich. Vienna, Vol. 6, pt. 1, pi. 7. Type, Tai. 

 (jSTaut.) quadrangulus, sp. McChesney, Trans. Chic. Acad., Vol. 1, 

 pi. 3, figs. 5-7, in Mus. Comp. ZooL. 



Mojsvaroceras 2 , nobis, of the Dyas and Trias includes the 

 species described by Mojsisovics in Mediterr. Trias ? Prov. as 

 Temnocheili. These have two rows of lateral tubercles, the form 

 quadrate and very stout, the siphons below the centre, and sutures 

 with ventral lobes, but also according to Mojsisovics with minute 

 annular lobes. Type, M. (Temno.) Neumayeri, Mojsis., pi. 88. 



Grypoceras 3 , nobis, includes species of the Triasjwhich are de- 

 scribed byMojsisovics, "Das Gebirge um Hallst.," with compressed 

 and more involute whorls than the above, abdomen, however, 

 truncated at some stage of growth, though acute in some 

 species in the later adolescent and adult stages. Siphon below 

 the centre, sutures like the above, but with deeper lateral lobes 

 and narrow V-shaped ventral lobes. The forms have annular 

 lobes according to Mojsisovics. Type, Gryp. (Naut.) mesodiscum, 

 sp. Hauer, Mojsis. ibid., pL 8. We include in this genus Gryp. 

 (Naut.) haloricum, obtusum and Gumbeli. ibid., pi. 7. 



Clydonautilus, Mojsisovics, Mediterr. Trias Prov. p. 281, 



1 Tcuvta, a head band. 



2 Dedicated to Mojsisovics von Mojsvar 



a Tpviro's, hook nosed. < 



