Hyatt.] 280 [April 4, 



Maelonoceratidae. 



This family includes shells with whorls in section ovate, very- 

 short living chambers, often more or less compressed or with con- 

 tracted apertures. The compressed apertures tend to become 

 fusiform, and the contracted apertures become pear shaped. 

 They are of smaller size than the Gomphoceratidae, and do not 

 grade into that group, but have their own radical, open-apertured, 

 cyrtoceran forms, which are included in the genus Maelonoceras. 

 The sutures have ventral, and dorsal saddles, and lateral lobes. 

 The siphons are near the venter and nummuloidal. 



Maelonoceras, 1 nobis, includes Silurian species with arcuate 

 cones, whorl in section compressed, ovate, the dorsum wider 

 than the venter. The siphon is near the venter. The sutures 

 have ventral and dorsal saddles, and slight lateral lobes. The 

 living chambers are short, and the apertures vary from entirely 

 open and partially subtriangular to contracted and pear shaped. 

 Type, Mael. (Phrag.) praematurum sp. Bill. Can. Nat. Vol. 5, p. 

 173, fig. 19. A close ally of this is Mael. (Cyrt.) discoideum, sp. 

 Barr. Syst. Sil. pi. 135. Mael. (Cyrt.) Metellus, sp. Bill. Pal. Foss. 

 p. 191, fig. 175, 176, is an open-apertured species. Mus. Geol. Surv. 

 Can. The genus may have arisen from the same common stock, in 

 Rizosceras but is certainly not a direct derivative of Acleistoceras. 



Oonoceras, 2 nobis, includes series of European forms, which 

 seem to arise from arcuate forms with open apertures, but more 

 elongated cones. They are annulated, and have even shorter and 

 more compressed living chambers in proportion to their longer 

 shells. They may either retain the open aperture, or produce a 

 fusiform outline in the opening. Oon. (Cyrt.) acinacies, sp. Barr. 

 pi. 118, Giebeli, pi. 123, exile and letheum, pi. 124, are examples 

 of cyrtoceran, and probably gyroceran forms, and Oon. (Troch.) 

 priscum and clava, pi. 12, oxynotum, pi. 14, anguis, pi. 16, are 

 examples of the closer coiled species There exist, doubtless in 

 other localities, congeneric, close coiled, symmetrical shells. These 

 Silurian forms lead into those with fusiform apertures, such as 

 Oon. (Cyrt.) multiseptatum, Roem. Paleontogr. Vol. 3, pi. 6, fig. 

 2, and Oon. (Phrag.) sub-ventricosum, sp. D'Arch. et Vern. Geol. 

 Trans. Vol. 6, pi. 30, of the Devonian. 



1 MtjXov, a goat. 



2 ttov, «n egg. 



