174 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



solete; beak pointed, incurved; umbo swollen. Sur- 

 face smooth or multicostate ; shell substance fibrous, 

 impunctate. 



Ventral interior. — Delthyrial cavity deep; teeth 

 strong, narrow, elongate; dental plates convergent, 

 forming a narrow spondylium, supported by a duplex 

 septum for part of its length; free at the front end. 

 Septum short. 



Dorsal interior. — Notothyrial cavity deep; crural 

 apparatus consisting of three pairs of plates intimately 

 united. At the posterior are two plates slightly convex 

 inward, uniting with the postero-dorsal wall of the 

 valve at the back and their dorsal or distal edges 

 uniting with the brachial supports. These form a sort 

 of hinge-plate. The sockets are excavations in the 

 lateral edges at the junction with the wall of the valve. 

 A second set of plates are set off from those above by 

 ridges. These are vertical, narrow, elongate bands 

 with their front ends free, and are supported by septa 

 which converge inward and unite directly with the 

 wall of the valve. Cardinal process simple, absent, or 

 present in some species. The diductors are usually 

 borne in a narrow pit under the beak. A low septum 

 divides the space between the septal plates into two, 

 and on each side of the ridge obscure adductor impres- 

 sions are visible. 



Geologic range. — Silurian and Devonian of 

 North America and Europe. 



American Species 



Gyfidula angulata Weller 1903 



G. coeymanensis Schuchert 1913 



G. coeymanensis frognostica Maynard 1913 



G.comis (Owen) 1852 



G. cornuta Fenton and Fenton 1924 



G. cornuta farva Fenton and Fenton 1924 



G. glo^ulosa (Netteholh) 1889 



G. /J«om(Nettelroth) 1889 



G. Ixviuicidus Hall 1867 



G. /o^M (Walcott) 1884 



G . mineolaensis Branson 1922 



G. multicostala HunhiT 1920 



G.nucleolata Belanski 1928 



G. nucleus (Hall and Whitfield) 1875 



G.occidentdis (HiW) 1858 



G.fafyracea Belanski 1928 



G. fseudogaleata recurrens Meyer 1913 



G.roemeri (Hall and Clarke) 1893 



G.romingeri Hall and Clarke 1893 



G.simflex Foerste 1909 



G.subglobosaMiymtdi 1913 



G. ««J/i/ici3/<3 (Nettelroth) 1889 



? G. fseudogaleata (Hall) 185 7 



Foreign Species 



Atry fa galeata Dilmzn 1828 

 Gyfidula dudleyensis Schuchert 1913 

 Pentamerus acutolobatus Sandberger 18 50-1856 



P. acutolobatus frocerula Barrande 1879 



P. caducus Barrande 1879 



P. globus 'i>c\^n\^T 185 3 



P. felagica Barrande 1879 (in part) 



Distinguishing characters. — Gyfidula is most 

 readily recognized externally by its galeate form and 

 the position of the fold on the ventral valve. Intern- 

 ally the differential characters are in the dorsal valve, 

 in the discreteness of the brachial supports, which form 

 a double track on the dorsal surface when the shell is 

 eroded or seen in section. 



Discussion. — ^The ventral morphology of Gyfidula 

 presents no departures from that in Clorinda, Pentam- 

 erella, and other genera of this subfamily. The septum 

 is exceedingly variable in its length and this is true like- 

 wise of the spondylium. The latter in some species 

 (G. romingeri and G. coeymanensis) is free for more 

 than three-fourths its length. The internal surface is 

 marked with elongate pustules and low ridges which 

 are interpreted usually as evidences of ovarian struc- 

 tures. The teeth are sharp and slender. 



The dorsal interiors of G. coeymanensis and G. 

 romingeri, of which excellent examples are at hand, 

 are especially instructive in illustrating the characters 

 of the genus. In these the dorsal septal plates are 

 divisible clearly into three parts, termed by Leidhold'* 

 (1) inner crural plates, (2) outer crural plates, and 

 (3) septal plates (see pp. 164-165). 



A linear cardinal process was observed by Hall and 

 Clarke in the genotype, but the occurrence of such a 

 structure is not general throughout the various mem- 

 bers of the genus. The usual condition is for the 

 diductors to attach to the floor of a deep pit under 

 the beak. It has been noted in some instances that 

 the pit is divided by a low ridge which may be inter- 

 preted as a cardinal process, although it was appar- 

 ently never functional as such in the sense of bearing 

 the muscles. 



Hall founded the genus Gyfidula on Petitamerus 

 occidentalis and G. Iwvtusculus and stated distinctly 

 that the lamella of the dorsal valve were separate and 

 diverging. This therefore excludes from Gyfidula 

 shells like Sieberella sieberi in which the septal lamellae 

 unite with a median septum. Hall and Clarke, reason- 

 ing with no knowledge of homceomorphy and the 

 confusion it may cause by obscuring the true relation- 

 ships of genera, maintained that the union or diver- 

 gence of the crural lamellas was of little import, being 

 only of specific value. In so holding, they could find 

 no distinction between the two genera except that 

 Sieberella was lacking in "deltidial plates" and a "car- 

 dinal area." This distinction between the genera has 

 been perpetuated by most recent authors. Schuchert in 

 1897 placed Sieberella in the synonymy of Gyfidula 



>' Abh. preuss. geol. Landesanst., N. F., Heft 109, 1928, 

 pp. 49-53. 



