504 
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 (Aug. precurrens), 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 costz on the sides and the promi- 
nent paired ventrolateral crests and corresponding lateral sinuses. 
The shell varies from that of Cyclolituites with whorls teuching 
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, z. ¢., 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 Zz¢. zbex., sp. Sowerby, certainly has none of the usual 
characteristics of any of this family. 
Trochoceras speciosum, Blake* has most extraordinary costz 
turned forwards as in the Lituitida, 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. 12-16. 
