GENERA OF THE SUBORDER PENTAMEROIDEA 



167 



Discussion. — Hall and Clarke say:" 



Whatever may be the oscillation in form and the varia- 

 tion in secondary characters presented by Camarella, Para- 

 strofhu and their allies, present evidence indicates that 

 they must be regarded as the genetic precursors, as they 

 are the secular precedents of the great group of true 

 pentameroids. 



And on page 355 they erect the family Camerellidre 

 for CamereUa, Parastrophui, Anastrophia, and ? Bran- 

 coma; all the other genera referred here by them are 

 now excluded from this family. 



Table 18 

 Camerellid^ 



Anastrophia 



Parastrophinella 



Metacamerella 



CamereUa 2, 



^ Branconia 



Syntrophiid^ 



Beecher and Clarke' have shown 



that in early age the shells of Anastrophia are normally 

 biconvex, and the brachial valve scarcely deeper than the 

 opposite. ... In this condition the form of the shell 

 resembles that of normal individuals of Camarella volborthi, 

 and in this series of forms, beginning in Camarella where 

 senile shells evince a gibbosity of the brachial valve and a 

 tendency toward reversion of convexity, and ending with 

 the Lower Helderberg Anastrophia verneuili, we have a 

 consecutive and gradational development in internal struc- 

 ture, which is accompanied by more abrupt variations in 

 exterior.*" 



As conceived by the present writers, the Camcrellidx 

 consist of shells in which the dorsal valve is usually 

 more convex than the ventral. The shells are com- 

 monly multicostate. The ventral interior has a promi- 

 nent spondylium duplex, but the most important family 



*Pal. N. Y., vol. 8, pt. 2, p. 341. 



» N. Y. State Mus., Mem. I, 1889, p. 32. 



" Hall and Clarke, op. cit., p. 225. 



characters arc in the dorsal valve in connection with 

 the cardinalia. The brachial processes are supported by 

 alate plates, concave outward, and these arc, in turn, 

 supported by septal plates which are cither discrete and 

 fastened directly to the floor of the valve as in Para- 

 strophinella and Anastrophia, or converge and unite 

 with a median septum to form a cruralium as in 

 CamereUa. Another feature of significance is the 

 attachment of the adductor muscles to the floor of the 

 dorsal valve entirely outside the septal plates. This is 

 a more primitive feature than in the derived Pentam- 

 eridas, in which the adductor muscles are confined 

 either within or on the dorsal septal plates or cruralium 

 when such a structure is present. 



The family as now constituted contains one genus, 

 Branconia, which is of doubtful value, and another, 

 Metacamerella, which has not been adequately de- 

 scribed. The former, which occurs in the Middle 

 Ordovician of Europe, is probably identical with Cam- 

 ereUa. Metacamerella, on the other hand, suggests an 

 Anastrophia, having a ventral fold, but the alate proc- 

 esses of the dorsal valve were not reported by the 

 nomenclator of the genus. 



In the Camerellidas the delthyrium appears to be 

 open or partially encroached upon by marginal growths 

 which have been called dcltidial plates, but they are 

 not like those in the Telotremata and it appears proba- 

 ble that true deltidial plates do not occur in this family. 



Genus CAMERELLA Billings 1859 



PI. 25, figs. 3-6, 8-13, 16, 20-22, 24, 27-30, 43 



Billings, Canadian Nat., vol. 4, 1859, p. 301. 



HaU and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 219, 



pi. 62, figs. 11-18 (Camarella). 

 Horn. Parastrofhia Hall and Clarke, Ibid., p. 221, pi. 63, 



figs. 1-3. 

 Syn. Parastrophina Schuchert and LeVcne 1929. 



Genolectotype (Hall and Clarke). — C. volhor- 

 thi Billings 1859. 



Description. Exterior. — Subglobular to subpen- 

 tagonal in outline; hinge-line narrow, cardinal ex- 

 tremities broadly rounded; profile unequally biconvex, 

 the dorsal valve having the greater convexity in mature 

 individuals; anterior commissure uniplicate. Ventral 

 interarea narrow, nearly obsolete; delthyrium open, 

 so far as known. Dorsal interarea obsolete. Surface 

 costate on the anterior half, smooth posteriorly. Shell 

 substance fibrous, impunctate. 



Ventral interior. — Delthyrial cavity deep; teeth 

 strong; dental and septal plates convergent to form 

 a spondylium duplex. Septal plates in conjunction 

 and prolonged in front of the spondylium for some 

 distance. 



Dorsal interior. — Notothyrial cavity deep and elon- 

 gate; brachial supports rather short and blunt; septa! 

 plates, which buttress the brachial support, elongate 



