Hyatt.] 304 [April 4, 



tes, Die Ceph. p. 64 pi. 1, 3. We, however, necessarily include in 

 Bactrites, such transitional forms as Bact. (Orth.) pleurotomum, 

 sp. Barr. pi. 296, Xanthus, Endymion, and caduceus, pi. 297, and 

 many other similar Silurian and Devonian forms. These have the 

 striae of growth raised into a saddle on the dorsal side, and the 

 siphon central, or when near the side, ventral as in Bactrites. 

 These forms, also, either have straight sutures or inclined sutures, 

 Bact. (Orth.) fasciolatum pi. 319, and Bact. (Orth.) obliquesepta- 

 tum, sp. Sand. Verst. Nass. pi. 18; but they do not have ventral 

 and dorsal saddles as in the compressed forms of Bactrites. Com- 

 pare for example Bact. (Orth) Paris and eximium, sp. Barr. pi. 

 412, with the similar compressed Bact. carinatus, sp. Munst. Sand. 

 Verst. Nass. pi. 17. Sandberger and Barrande agree in their 

 observations and in their opinion, that the ventral lobe is due to 

 the approximation of the funnels to the side in Bactrites, and 

 the facts support this conclusion. The Silurian forms we have 

 mentioned are evidently the radicals of Bactrites, and we can 

 only account for their affinities in form, in the transverse striae, 

 and sutures with Mini, compressum by referring both to the com- 

 mon stock and imagining them as the more direct descendants 

 of that stock, which must have had banded shells similar to those 

 of Geisonoceras. The aspect of the apex in two specimens of 

 Bactrites Hyatti, in the Museum of Munich, show that Bactrites 

 is probably a true Nautiloid in the earliest stages, but this dis- 

 tinction has lost much of its value since the discovery of the 

 protoconch in some of the straight cones. It leaves us still at 

 liberty to give due weight to the transitional characteristics of 

 the later stages. And we must, also, in this connection call atten- 

 tion to the important transitional character of the cicatrix, which 

 is shown in our figure of Bactrites on M. Barrande's pi. 490. 

 The cicatrix is unusually large and indicates a protoconch with a 

 larger neck than is usual among Nautiloids. We have seen some, 

 perhaps, even larger in proportion, but they are exceptional as M. 

 Barrande shows in his figures. These facts show, that the ven- 

 tral lobe of Bactrites is an independent production in this series 

 of straight cones. At the same time we should not forget that 

 such parallelisms occur only in nearly related series, which are 

 descended from the same common stock. At least this has been 

 our experience in all the series we have traced, and we are, there- 



