1883.] 317 [Hyatt. 



compressed and subacute in several species, but retain their open 

 umbilici except in the most involute species. In these, however, 

 the larvae remain sufficiently constant to enable us to recognize 

 the genus. The serrated or costated abdomens of the young of 

 several forms, is also in marked contrast with Manticoceras. The 

 depth of the ventral lobes causes the septa to assume a convex 

 aspect, but the median line remains concave until a late stage of 

 growth. The large lateral saddles when first formed, and until 

 a comparatively late stage in radical species, have no correspond- 

 ing dorsal saddles, these arise later as two minute saddles in the 

 dorsal lobe, on either side of the annular lobe. The species are 

 Geph. (Gon.) calculiforme, Beyr. Sandb. Verst. Nass. pi. 8, fig. 

 9-9a (not 9c-d), aequabile, Beyr. Gon. Mont. Rhen. pi. 2, fig. 1, 

 and also Sandb. pi. 8, fig. 10, to which last also belong Sandberg- 

 er's figures 9c-d mentioned in brackets above, Hoeninghausi, 

 D'Arch. et Vera.. Trans. Geol. Soc. Vol. 6, n. s. pi. 25, and Buchii, 

 ibid, pi. 26, fig. 1, serratum, sp. Sandb. pi. 9, fig. 8, planorbe ; sp. 

 Sandb. pi. 9, fig. 3, forcipifer, sp. Sandb. pi. 6, fig. 3, discum, 

 Roem. Nordw. Hartz. Paleontogr. Vol. 6. pi. 13, fig. 35 (not pi. 

 6, fig. 7) and bisulcatum ibid, pi. 6, fig. 8, acutum, Keyser, Dom. 

 Schief. Verh. Mimneral. Gesell. St. Petersb. 1844, pi. A fig. 6. 

 In America we have seen only Geph. (Gon.) complanatum, sp. 

 Hall, Nat. Hist. N". Y. Vol. 5, pi. 70, fig. 6-12, and the Type, Geph. 

 sinuosum, ibid, pi. 70, fig. 73-75, Mus. Geol. Surv. Albany. 



Manticoceras, 1 nobis, includes species with compressed and 

 often very involute whorls, which are, however, directly traceable 

 by the closest gradations into forms with broad whorls, open um- 

 bilici, and an aspect similar to that of Anarcestes. The young 

 are invariably less discoidal than in Gephuroceras, the abdomens 

 rounded, and the sides divergent outwardly. A close resemblance 

 to Agoniatites bicaniliculatus, or tuberculosocostatus 2 occurs in 

 the costated young and in the sutures and form of Mant. triparti- 

 tum until a late larval stage. The adult sutures have the same 

 general aspect as those of Gephuroceras, but the septa in the 

 compressed involute forms become more decidedly convex. The 



1 MavriKo's, prophetic. 



2 This is a costated species of Agoniatitites, which we have supposed to be equiva- 

 lent to Sandberger's figure Verst. Nass. pi. 2, fig. 3. It also resembles costulatus 

 D'Arch. et Vera. Trans. Geol. Soc, pi. 26, fig. 8. 



