NO. 5 RHYNCHONELLOID BRACHIOPODS — COOPER IO, 



Discussion. — This genus differs strongly from other modern and 

 Tertiary rhynchonelloids except Mannia which is discussed below. 

 The form of the median septum and crura are unique and the deltidial 

 plates are formed differently from those of the other rhynchonelloid 

 genera. 



The deltidial plates of Cry p top or a are disjunct throughout life. The 

 foramen is not greatly restricted by these plates because they usually 

 grow at a high angle to the edge of the delthyrium rather than being 

 a continuation of it. The foramen is thus incomplete and not circular 

 but is deltoid and roughly parallel to the delthyrial margins. 



The deltidial plates are small and elongate triangular, forming on 

 the delthyrial margin at a high angle and commonly reflected laterally 

 to overhang the dorsolateral slopes of the beak. In Cryptopora rec- 

 timarginata Cooper, new species, the deltidial plates are strongly 

 alate, the projections being located near the posterior of the plate and 

 narrowly rounded, bluntly pointed or rarely serrated. In the older 

 shells the blunt points disappear. 



The apex of the pedicle valve is occupied by a small elevated tri- 

 angular plate against which the pedicle rests. A plate similar to this 

 appears in other genera, such as Hemithyris. Aside from the strong 

 dental plates the pedicle valve reveals no other structures. The shell 

 is so thin that muscle scars cannot be seen easily. A suggestion of a 

 low myophragm appears in some specimens. 



The cardinalia of the brachial valve are unusual. The socket plates 

 are small and delicate, appear to be continuous with the crural bases 

 and lie above or posterior to them. The socket plates are attached 

 directly to the shell wall and buttressed for a short distance by a small 

 supporting plate. The crura are long and welded with the crural bases 

 and supporting plates in such a way that they appear to make one 

 plate. The main part of the crura are strong but slender and are 

 bowed outward to a considerable degree in older specimens, less so in 

 the young ones. The distal extremity is flattened laterally and the free 

 end serrated or frayed into a number of small prongs. The whole 

 suggests a tiny hand with outstretched spreading fingers or a flattened 

 fist. 



The diductor muscles were attached to a bilobed boss or cardinal 

 process at the posterior apical part. This is somewhat thickened in old 

 shells, the thickening spreading to the base of the crura and uniting 

 with an extension of the median septum. 



The most conspicuous feature of the brachial valve is the median 

 septum. It is highest at about midvalve but descends rapidly posteri- 



