BUCHICERAS ( SPHENODISCUS ) BELVIDERENSIS 

 AND ITS VARIETIES. 



By F. W. Cbagin. 



SpHENODISCUS BELVIDERENSIS. Crag. 



Shell of medinin size, flattish-leuticular, the venter (per- 

 iphery) truncate, narrowly so on the younger whorls, broadly 

 and less sharply and less evenly so on the oldest one, particu- 

 larly on the body-chamber; body-chamber occupying three- 

 eighths toone-half of a vcjlution ; umbilicus narrow, the greater 

 part of the height of the second whorl being embraced within 

 one-third to one-half of that of the body-chamber; suture 

 '• ceratitic," much like that of SpJtc.iiodiscns pedcrndlis, Von 

 Buch, the part corresponding to the outer saddle of (strictly 

 so-called) Bnchiceras being divided into five saddles by means 

 of four leaves, of which the very unequal outer two are much 

 smaller than the subequal inner two; all of the saddles of 

 the suture rounded to llattish or, in case of some of the inner 

 ones, emarginate at fundus, some symmetrically, some ob- 

 liquely so, and all much broader than the leaves, excepting 

 the next to the outermost of those formed by the lobing of 

 the outer buchiceran saddle; the leaves little cleft at the 

 summit; ornamentation of the shell consisting usually of at 

 least two revolving series of low tubercles on either side: one 

 just outside of the umbilical shoulder, and consisting of few 

 tubercles, one or two of the newer of which sometimes be- 

 come more prominent than any other tubercles on the shell; 

 the other, presented ventrally on the ventro-lateral margin, 

 and consisting of numerous tubercles so compressed as to 

 trend with that margin, and so arranged that those of the riglit 

 alternate with those of the left margin, half (consisting of 

 every other one) of these tubercles constituting the termini 

 of broadly and feebly accentuated lateral ribs, which are con- 

 fined to the outer part of the tlank, and at whose inner ends 

 (one at the end of each) the very low and diffuse tubercles 

 of a third n-volving series may be developed. 



