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tral and dorsal crests and lateral sinuses in its lines of growth that 

 are first observable in the degenerative stages of the ontogeny o 

 allied and more complicated shells (Ang. fircecurrens) , it includes 

 in other words some species at least that are purely phylopara- 

 gerontic. 



No genus of this family, except Cyclolituites, has an impressed 

 zone, the transverse section being round or more usually a com- 

 pressed oval ellipse. The most obvious external characteristic, 

 which fails of being distinctive only in some species of Angeli- 

 noceras, and in them in the ephebic stage only, is the forward cur- 

 vature of the lines of growth and costae on the sides and the promi- 

 nent paired ventrolateral crests and corresponding lateral sinuses. 



The shell varies from that of Cyclolituites with whorls touching 

 until a late ephebic stage, only a part of the living chamber being 

 free, through forms like Lituites with a portion of the camerated 

 whorl and the whole of the living chamber free and straight, to 

 Rhynchorthoceran forms which have uncoiled whorls. 



The apertures vary, but possess in Lituites, Ancistroceras and 

 Cyclolituites, prominent ventro-lateral crests and deep ventral 

 sinuses. 



The siphuncle is large and subcentral, central or just above the 

 centre and in the young approximates to the dorsum. It is, so far 

 as known, ellipochoanoidal and microchoanitic, i. e., composed of 

 short funnels that are directed towards the apex and having porous 

 walls between the funnels and the next septum. 



All of these forms known to me occur in the Orthoceran and 

 Varginatus limestones of Northern Europe and Niagara limestones 

 and Quebec faunas in this country. They seem to be absent from 

 more southern faunas of the same stages. 



Foord doubts the appearance of true Lituites in the rocks of Great 

 Britain, and I think he could have positively denied their appearance 

 there since Lit. ibex., sp. Sowerby, certainly has none of the usual 

 characteristics of any of this family. 



Trochoceras specioswn, Blake * has most extraordinary costae 

 turned forwards as in the Lituitidae, but the siphuncle is ventral 

 and the description is inadequate, and at variance with the figure 

 so that one cannot arrive at any definite conclusion. 



*Brit. Ceph., PL xiv, Figs. 12-15. 



