GENERA OF THE SUBORDER PENTAMEROIDEA 



171 



duplex, supported by cither very long or short double 

 septa; but in two genera the spondylium hangs free. 

 Dorsal cardinalia — the most characteristic feature of 

 the family — tripartite; consisting of discrete plates, or 

 united into a cruralium that bears the adductor muscles. 

 When the plates are discrete, the adductors are on the 

 floor of the shell between them. Brachial processes 

 very long, and in some forms terminally divergent. 

 A cardinal process is usually absent or, when present, 

 is a rudimentary septum or a low callosity. A concave 

 deltidium and incipient deltidial plates are sporadically 

 developed, but in general the delthyrium is open. 

 Shell substance fibrous, impunctate. 



Geologic range. — Silurian and Devonian. 



Embraces two subfamilies: Gypidulins Schuchert 

 and Pentamerinae Waagen. 



Discussion. — The Camerophoriina; of the Devo- 

 nian and Carboniferous, long included in the Penta- 

 meracea, are now considered to be spondylia-bearers of 

 the Rhynchonellacea, and the Porambonitidas are in the 

 present work shown to be much modified Orthacea. 



Subfamily GYPIDULIN^ Schuchert 1929 



Pentamerids more or less galeatiform, with small 

 ventral interareas. Ventral valve always the more con- 

 vex and deeper. Cardinal process simple, but usually 

 absent. Shells smooth, or with some low or many 

 rounded costae. 



Geologic range. — Silurian and Devonian. 



Includes the following genera:'^ 



Clorinda Barrande (syn. Barrandina Booker 



1926) 

 Barrandella Hall and Clarke 

 Gyfidula Hall 

 Sieberella Oehlert 

 Pentamerella Hall 

 ? Zdimir Barrande 



The genetic relations are about as shown in Table 

 19. 



Discussion. — We include in the subfamily Gypidu- 

 linae all of the galeatiform Pentameridae having the 

 internal structure of the family. This subfamily was 

 rather prominent in the Silurian and Devonian but 

 evidently did not survive the latter period. As pre- 

 viously constituted, it included Virgiana, but the struc- 

 ture of the dorsal septal plates in the latter genus is so 

 close to that in Pentamerus that it must be referred 

 to the Pentamerinae. Its previous constant association 

 with the Gypidulinje is undoubtedly due to the errone- 

 ous figure of the interior published by Hall and Clarke. 



" Our genus Lioccetia, which was included in this sub- 

 family in 1931, is now seen to be a rhynchonellid; it is 

 further described in the Appendix to this work. 



Clor'ttida and Barrandella show some internal varia- 

 tions from the rest of the subfamily. At the junction 

 of the inner and outer septal plates of the dorsal valve 

 there is a small process extending in a ventral direction 

 and into the notothyrial chamber. This feature has 

 not been observed in Gyp'tdtda, Sirherella, or Penta- 

 ?nerclla, but was noticed in one specimen of Clorinda. 

 In the Gypidulinae occur some interesting paral- 

 lelisms. Barrandella and Clorinda are externally alike 

 but in the former the plates of the dorsal valve form a 



Table 19 



Gypidulin^ 



Pentamerella 



Pentamerin* 



Barrandella 



CAMERELLIDiC 



cruralium whereas in the latter they are discrete. The 

 same relations also hold for Sieberella and Gypidula. 

 These striking features are not only of great interest 

 but are of considerable importance to students of strati- 

 graphy and paleogeography. 



Genus CLORINDA Barrande 1879 

 PI. 26, figs. 8-12, 21; t. fig. 29 



Barrande, Syst. Sil. Boheme, vol. 5, 1879, p. 109, pi. 1 19, 



figs. 1-4. 

 Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 244. 

 Syn. Barrandina Booker 1926 (genotype, B. wilkinsoni 



Booker 1926 ^ Pentamerus linguifera var. wilkinsoni 



Etheridge 1892 (pars)), Jour. Proc. Roy. Soc. N. S. 



Wales, vol. 60, p. 131. 



Genoholotype. — C. armata Barrande 1879. 



Description. Exterior. — Subgaleatiform ; hinge- 

 line straight, cardinal extremities broadly rounded; 

 lateral profile biconvex, the ventral valve having the 

 greater convexity. Anterior commissure uniplicate; 

 ventral sulcus usually ill defined; anterior of ventral 



