142 SOME NEW SPECIES OF AMMONITES, 



in its flatter ventral area, especially near the termination its 

 finer and more numerous ribs, and several other points. 



The specimen figured has the greater portion of the test very 

 well preserved. 



SPHAEROCERAS PEREXSPANSUM, Nbbis, plate ii., fig. 4 a-b. 



Shell globose ; very wide. Whorls few, and entirely occluded. 

 Primary ribs small, numerous, rounded, extending on the ventral 

 area before bifurcating. 



This species is somewhat scarce, and I only know of a few 

 specimens from near Sherborne, Dorset, collected by my father. 



Position, probably zone of Stephan. Humphriesianum. 



Nearest Allied Form. Sphaeroceras Manselii, but our species 

 differs from it on account of its far greater width and more con- 

 vex ventral area. 



These two last species, together with Sphaer. Bronginarti, 

 Sphaer. Gervillii, &c., seems to form very well a genus easily 

 separable from that of Stephanoceras, although connected with 

 it by one form, viz., Stephanoceras, Sauzei. In my paper to 

 the Geological Society I placed Stephan. Sauzei in the genus 

 Sphaeroceras, but I have since seen reason to take another view 

 mainly on these grounds : Sphaeroceras, as far as I have examined 

 has no proper labial prolongations of the mouth-border, but only 

 a semi-lunar band more or less complicated. It does not possess 

 spines at the junctions of the ribs, the primary dividing quite 

 plainly into secondary. The umbilicus, especially when young, 

 is very much closed, and the shells are generally very globose. 

 The body-chamber in Sphaeroceras, is, as far as I have examined, 

 nearly a whorl in length. 



Stephan. Sauzei it will be seen though in general shape allied 

 to Sphaeroceras does not correspond to the other particulars. 



Stephanoceras has both kinds of terminations, the labial pro- 

 longations, and the semi-lunar band. 



The genus Sphaeroceras is continued in the Great Oolite with 

 Sphaer. bullatum, Sphaer. microstoma, &c. 



