The Invertebrate Fauna of the Uitenhage Series. 101 



of the valve margin is smooth, in the anterior part of the shell at 

 least. If there is any crenulation at all, it is confined to the posterior 

 half of the valve, and must be of a weak description. 



Dimensions. (1) (2) (3) 



Length (estimated) 78 . 84 135mm. 



Greatest height 53 . 58 92 ,, 



Greatest depth of a single valve 19 . 23 . 32 ,, 



Occurrence. Obtained by Mr. Rogers from a bare slope W. 30 S. 

 from the middle of Barkly Bridge, on the farm Olifant's Kop, 

 Sunday's Eiver (20h) ; also from Coega Valley, east of the railway, 

 one mile up the line from Coega station (472g). 



Remarks. This is an elongated representative of the section 

 Scabrae, and, generally speaking, it exhibits the normal characters 

 of the section. It is remarkable, however, for its very large size and 

 for the manner in which it shares the character of posterior elonga- 

 tion with other Trigonice from the Uitenhage beds and from the 

 Oomia beds of Cutch. This prolongation at the siphonal end, and 

 the absence of sculpture from the area in the later adult stages are 

 characters similarly shown in members of the group of Trigonia van 

 and in T. conocardiiformis (Uitenhage Series) and in members of the 

 group of T. v-scripta and certain degenerate Costatas (in the Oomia 

 beds). There are evidences of degeneracy in all these forms. In the 

 specimen numbered (2) in the above table of measurements, one valve 

 is almost complete at the siphonal border, and the form of the valve 

 at that part suggests that in the complete shell a slight posterior 

 gape may have been developed, just as in T. stowi. 



In the neanic and early adult stages, T. rogersi bears a consider- 

 able resemblance to the same stages in T. ventricosa (Krauss). It 

 differs, however, in details of the sculpture on the area and escutcheon, 

 and with advancing growth, the characters of outline, degree of 

 inflation, and ribbing of the shell are so widely distinct in the two 

 forms as to need no comparison here. 



TRIGONIA HERZOGI (Goldfuss). 



Plate V., fig. 1. 



1837. Lyrodon herzogii (Hausmann) A. Goldfuss, Petrefacta 

 Germanise, Band ii., Lief. 6, p. 202, Tab. cxxxvii., 

 fig. 5. 



1850. Lyrodon herzogii F. Krauss, Nov. Act. Acad. Caes. Leop.- 

 Carol. Nat. Cur., vol. xxii., pt. 2, p. 453, Tab. 48, 

 r fig. 3. 



8 



