Hyatt.] 272 [April 4, 



are generally smooth but may be either annulated or striated 

 longitudinally. The sutures are generally more arcuate than in 

 the Orthoceratidae, and the cones stouter in proportion to their 

 length. 



Actinoceras, Bronn, has several subdivision whose natural 

 order seems to be as follows. Sub-genus Discosorus, Hall, Nat. 

 Hist., 1ST. Y., Vol. 2, pi. 28, includes isolated siphons apparently 

 inseparable from the siphons of Actinoceras, but having some 

 doubtful characteristics. They may be brevicone forms of the 

 Actinoceratidae, as suggested by Barrande. Orth. infelix sp. 

 Bill., seems to be in form at any rate an intermedium to Actin- 

 oceras, if the apex or young siphon was broken off, it would be 

 difficult to separate it from Discosorus. Actinoceras, Bronn, 

 Leth. Geog., 1834, equals Ormoceras, Stokes, 1837, Trans. Geol. 

 Soc. Lond. 2 ser., Vol. 5. Conotubularia, Troost, Mem. Soc. Geol. 

 France, ser. 3, pt. 1, p. 89. 1 The rosettes are globular and com- 

 pressed, always discontinuous. The planes of discontinuity occur 

 between the sej)ta and are marked by tubes and spaces radiating 

 from the long, central tube. This tube was in life occupied by 

 a fleshy sheath at its anterior part, which was derived from the 

 large siphon by shrinkage of its fleshy walls and was continued 

 backwards into a still more shrunken part forming a long endo- 

 siphon, but not having a special wall as in Endoceratidae. The 

 endosiphon, or fleshy shrunken siphon, was swollen at intervals 

 between each septum and gave rise to flattened attenuated rings 

 of membrane, which had radii of solid cords, or tubes, and 

 often the ring became partly resorbed and these tubes or cords 

 were alone left between the rosettes. They do not appear to 

 penetrate the true external or sheath wall of the siphon. M. 

 Barrande has already shown all of these facts clearly, we differ 

 only on minor points. That eminent author regarded the rosettes 

 as not homologous with the sheath of Endoceras though secreted 

 by the same organ, namely a modified fleshy siphon. We regard 

 the rosettes as internal, or extra endosiphonal deposits, and the 

 successive sections of the outer wall of the siphon as strictly 

 strictly homologous with the successive sheaths of the endosiphon 

 of Piloceras and Endoceras. The Mus. Geol. Surv. Canda., 



1 Conilites, Pusch, Polen's Pal. p. 150 is supposed by Barr. and others to be also a 

 synonym of Actinoceras. 



