Hyatt.] 276 [April 4, 



same author. It includes all those longicone species m which the 

 ridges become spiny, or are roughened by the prominence of the 

 transverse striae or ridges. Silurian ? Devonian, Carboniferous. 



Spyroceras, 1 nobis, includes the longitudinally ridged longi- 

 cones, which at some stage of their growth are also annulated. 

 The annular costae are usually large rendering the outline sinuous. 

 The longitudinal ridges are present in the young, and the annular 

 costae are developed later. Includes groups 5, 6 of M. Barrande. 

 Type, Spy. (Orth.) crotalum, sp. Hall. Mus. Geol. Survey, Albany, 

 N. Y. Silurian and Devonian. 



Dawsonoceras, 2 includes forms like D. (Orth.) pseudo calami- 

 teum, sp. Barr., pi. 286, and others which have longitudinal 

 ridges in the larva and are annulated, but devoid of ridges in the 

 adolescent and adults. The type is related to the series with 

 laro-e annulations and frilled transverse striae, sometimes with 

 longitudinal ridges, though the young in D. (Orth.) dulce, sp. 

 Barr., pi. 275 have no longitudinal ridges. The apertures have 

 flaring lips as in Halloceras. Type, Daw. (Orth.) annulatum, Mus. 

 McGill College, Montreal. 



Rizosceras, 8 nobis, includes the straight cones figured by M. 

 Barrande, Vol. 2, pis. 185-195, having simple sutures, and septa, 

 and banded shells, whorl in section elliptical. The form is 

 remarkably short, and increases very rapidly, the living chamber 

 short, and widely flaring, with shallow ventral sinus. The siphon 

 is variable in position, but is rarely near the centre. Type, Riz. 

 (Orth.) indocile, pi. 185, figs. 1-6. We include in this group, 

 also, such forms as are intimately connected with Rizosceras, like 

 Riz. (Cyrt.) corniculum, pi. 121, sp. Barr., and (Cyrt.) apertum 

 sp. Barr. pi. 146. 



The larger part of the forms figured by Barrande, pis. 1-158, 

 belong to our genus Maelonoceras, and to various other groups, 

 pis. 149-153, however, exhibit almost exclusively cyrtoceran, 

 forms with rizosceran affinities. An extreme form of this genus 

 is the Riz. (Phragm.) imbricatum, sp. Barr. pi. 175. This group 

 can also be subdivided according to the character of the siphon, 



1 Einpts, a basket. 



2 Dedicated to Dr. J. W. Dawson of Montreal. 



8 PCsa, a root. 



