1883.] 285 [Hyatt. 



Rutoceras 1 , nobis, includes arcuate, Devonian forms closely 

 allied to Zittelloceras in the imbricated structures, and flaring 

 apertures of the shells, but having three rows of large nodes on 

 either side. The siphon is ventral, but it is large and nummu- 

 loidal instead of being tubular, and small. The living chambers 

 are shorter than in Zittelloceras, and the form in section is de- 

 pressed elliptical. Type is Rut. (Cyrt.) Jason sp. Hall, Nat. Hist. 

 N". Y., Vol. 5, pt. 2, pi. 50, and supp. pi. 124. This genus also 

 includes shells similar to the above, but having the gyroceran 

 form, and less rugged surfaces. The abdomen becomes more 

 elevated and slightly narrower, the dorsum slightly flatter, and 

 broader than the venter. 



Triplooceras 2 , nobis, includes the remarkable Silurian species 

 Tri. (Naut.) insperatum sp. Barr. Syst. Sil., pi. 461, which has 

 whorls in section like those of Rutoceras, and similar sutures, but 

 with very slight ventral lobe, and the typical three lines of tuber- 

 cles on either side ; siphon between centre and venter. 



Adelphoceras, Barr. ibid, Text 3, p. 788, et suppl. pi. 459, 

 also Silurian, has three lines of tubercles on either side, and 

 though the aperture is contracted as in Gomphoceras, we include 

 it provisionally in this series. Siphon ventral. 



KLophinoceras, 3 nobis, includes Devonian species, which have 

 rough shells as in Rutoceras, and numerous ridges on the abdo- 

 men, more or less roughened or broken in adults by nodes formed 

 by the permanent lips of the apertures. The species vary greatly, 

 but are all probably gyroceran, and the normal forms have either 

 two rows of tubercles along the middle of the venter, or a 

 broad raised band as in some Halloceratites. There are also two 

 rows of nodes along the angle of the junction of the sides and 

 abdomen, which are large and persistent. The form in section is 

 more depressed than in Rutoceras, the siphon nummuloidal, and 

 ventral ; sutures with ventral saddles, and in one species a small 

 annular lobe. The type, Koph. (Cyrt.) ornatum, sp. D'Arch. et 

 Vern. Trans. Geol. Soc. Lond., Vol. 6, pi. 28, Mas. Comp. Zool., 

 Camb. has three persistent rows of nodes open to the front, or 



i PvIst, a fold. 



2 TpiirXo'os, three-fold. 



8 Ko'4>kVOs, a basket. 



