1883.] 273 [Hyatt. 



contains species which are apparently transitional to Huronia, 

 as stated by Billings, but these species have large endosiphons, 

 and the Actinoceran type of rosettes, and the siphons resemble 

 those Of Huronia merely in the external form of the rosettes. 

 The genus is found in the Carboniferous, Act. (Orth.) gigan- 

 teum, sp. Sow. De Kon. Calc. Carb., pi. 44, and throughout the 

 Paleozoic. From typical Actinoceras the transitions are insensible 

 into the forms of the next group. 



Sub-genus Deiroceras, 1 nobis, has the septa more widely sepa- 

 rated than is usual in Actinoceras and parts of the siphon between 

 the septa assume a globular form. The rosettes are more irregu- 

 lar in their formation than in that genus, and the cavity of the 

 endosiphon is an irregular narrow tube. The rings, and cords or 

 tubes of the siphon are more abrupt at their junction with that 

 tube, and more attenuated. Actin. (Orth.) crassiventre, as figured 

 by Barr., pi. 237-233, is a transition form to typical Actinoceras. 

 Act. Putzosi, ibid., pi. 211, 235 is very close to the type of this sub- 

 genus, A. (Orth.) python sp. Bill. Mus. Can. Geol. Surv. The tran- 

 sition to Huronia occurs through these forms. 



Sub-genus Huronia, Stokes, Trans. Geol. Soc. Lond., ser. 2, 

 Yol. 5, p. 705, is similar to the preceding, but has the septa more 

 widely separated and only the posterior zone of each rosette is 

 globular, the anterior zone of each rosette being tubular, with 

 a swollen rim. It may be, also, that in this sub-genus the endo- 

 siphonal rosettes are habitually continuous. The endosiphonal 

 tube is narrow and regular. Passing back to the radical form 

 Actinoceras, we find that M. Barrande has traced a natural series 

 in his preface to his second series of plates No. 245-350, p. 9. 

 In his list, Act. vertebratum, cochleatum, crassiventre, imbri- 

 catum, Clouei are in our scheme true Actinocratites, and we draw 

 our artificial generic line between the last species, and Sactoceras 

 exoticum. 



Sactoceras, 2 nobis, includes species in which the septa are in 

 most species approximate as in Actinoceras, and the siphon num- 

 muloidal, but much reduced in diameter. This is the result of 

 a reduction in the size of the fleshy siphon near the living 



1 Acipr), neck. 

 * SaKTos, stuffed. 



PHOCKEDIMGS B. S. N. H. VOL. XXII. 18 JANUARY, 1884. 



