172 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



valve produced into a long tongue; dorsal fold low, 

 best defined at the front. Ventral interarea narrow 

 and short, curved apsacline to orthocline, beak strongly 

 curved, umbo inflated; dorsal interarea obsolete, beak 

 curved, umbo swollen. Valves unornamented except 

 by concentric lines of growth. Shell structure fibrous, 

 impunctate. 



Ventral interior. — Delthyrial cavity shallow; teeth 

 small, dental and septal plates forming a small spon- 

 dylium duplex, which is free at its anterior end. 



Dorsal interior. — The septa of the dorsal valve are 

 subparallel or divergent as in Gyfidula. At the junc- 

 tion of the inner plates with the base of the brachial 

 process there is a carina pointing ventrally. The 

 brachial process is wide, moderately long. 



Geologic range. — Silurian of North America, 

 Europe, and Australia. 



and accordingly we feel that this carina has no signifi- 

 cance in generic taxonomy. A plate of this kind was 

 seen also in one specimen of C onchidium, and Booker 

 shows them as well in Gyfidula galeata from Gotland. 

 We therefore hold that Clorinda is the smooth equiva- 

 lent of Gyfidula, having its fold on the dorsal valve. 

 In this latter respect it differs from certain smooth 

 Gypidulas (G. fseudo galeata^ which may ultimately 

 be referred to a new subdivision. 



Booker has recently proposed a new genus Bar- 

 randina for shells having the external form of Clorinda, 

 but thought to differ from the latter in the dorsal 

 interior. He defines his genus in part as follows: 



At the junction of the crural plates and septa a pair of 

 curved, outwardly convex plates are developed. These are 

 attached throughout their entire length to the cruralium, 

 at the junction of the crural plates [inner plates] and septa 





1^. ^'^ 



Fig. 29. — Serial sections of Clorinda fseudoUnguijera Kozlowski. After Kozlowski. ca, carina at the limit of crural 

 plates and crural septa; cr, crural plates (inner plates); dt, teeth; scr, crural septa (outer plates); sm, spondylium; 

 s, septum. 



American Species 

 Athyris {?) tumidula Billings 1866 



European Species 



Clorinda ancillans Barrande 1879 



C. armata Barrande 1879 



C. bubo Barrande 



C. fseudoUnguijera Kozlowski 1 929 



Distinguishing characters. — Clorinda is a 

 smooth shell, internally resembling Gyfidula, and hav- 

 ing the fold on the dorsal valve. 



Discussion. — Inside the ventral valve the septum 

 is very short and the spondylium hangs free for most 

 of its length. The dorsal cardinalia are like those of 

 Gyfidula and have rather long brachial processes as is 

 typical of the family. The most notable distinction 

 to be seen from Gyfidula is the carina which runs 

 along the base of the brachial process at its junction 

 with the inner plate. In pentamerids of this type from 

 Australia a carina may be seen also at the junction of 

 the base of the brachial process with the outer plate. 



[outer plates], either along the median line of the convex 

 side of the plate, or at the edges, being then intercalated 

 between the septa and crural plates. These plates extend 

 beyond the anterior termination of the crural plates and 

 septa for fuUy one-third of their length and terminate at 

 a point slightly anterior to the end of the spondylium. 



The sub-genus Barrandina has been erected for the recep- 

 tion of certain Australian Pentamerids, with the fold on 

 the brachial valve and sinus on the pedicle valve, in which 

 the cruralium is modified by the development of an extra 

 plate at the junction of the septa and crural plates. The 

 two species comprising the sub-genus were first described 

 by Etheridge as Pentamerus linguifera var. zvilkinsoni. 

 Subsequent work on the pentameroids of the Yass district 

 has revealed a series of forms paralleling in their structures 

 the Barrandella and Sieberella series of Europe and America, 

 but all characterized by the development of an extra plate in 

 the cruralium. 



It is our belief that the "extra plate" of Booker is 

 actually the same as the brachial process of all other 

 pentamerids but has more pronounced ridges than is 

 usual along the junction of the inner and outer plates 

 with the base of the brachial process. In our opinion 

 the internal structure of Barrandina does not differ 



