118 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



The genotype is the only known species and comes 

 from the Canadian (Walchow) in the vicinity of 

 Leningrad. 



Subfamily GONAMBONITIN^ Schuchert and 

 Cooper 1931 



Aberrant Clitambonitids having a strophomenoid or 

 substrophomenoid profile and a sessile spondylium 

 (pseudospondylium). Dorsal and ventral median 

 septa are lacking. In the species studied by us the del- 

 tidium is imperforate. 



The subfamily embraces only the one genus, 

 Gonamhonites Pander. 



Genus GONAMBONITES Pander 1830 

 sensu lato 



PI. 8, figs. 1-5, 7, 20, 21, 25, 26 



Pander, Beitr. Geogn. Russ. Reiches, 1830, p. 77, pi. 3, 



fig. l,pl. 16a, fig. 3, pi. 28, fig. 15. 

 Opik, Acta et Comment. Univ. Tartuensis, A, vol. 1 7, 



pt. 1, 1930, pp. 220-222. 



Genolectotype (Schuchert and LeVene). — G. 

 lata Pander. 



Description. Exterior. — Shell strophomenoid or 

 substrophomenoid in appearance, semielliptical ; hinge- 

 line wide and straight, cardinal extremities acutely 

 angular; lateral profile convexo-concave; lateral com- 

 missure flexed dorsally; anterior commissure slightly 

 sulcate, there being a faint sulcus in the dorsal valve. 

 Ventral interarea the longer, plane, strongly apsa- 

 cline; dorsal interarea short, apsacline to anacline. 

 Deltidium imperforate in G. -planus; notothyrium 

 closed by a chilidium. Ornamentation multicostellate. 

 Shell substance fibrous, impunctate. 



Ventral Interior. — Delthyrial cavity deep; teeth 

 small; spondylium (.'' pseudospondylium) sessile and 

 strengthened on each side by a short lateral septum or 

 several septa.®^ 



The muscles were attached to the upper surface of 

 the spondylium. The adductor tracks are linear. 

 Diductor and adjustor scars can not be differentiated 

 but the combined marks are situated on the sides of the 

 dental plates. Subperipheral rim low. 



•^ A note in regard to the spondylium (?) of G. flanus 

 will be of interest. This is sessile and strongly suggests the 

 pseudospondylium common to Finkelnburgia and Linofor- 

 ella. The extra "supporting plates" are directly ventral to 

 the dental plates and may actually be a continuation of 

 them, and the floor of the spondylium may therefore be 

 composed of callus. We had before us no very young shells, 

 from which the true character of the spondylium could be 

 ascertained. Should this ventral muscle field prove to be 

 a pseudospondylium, the relationship of Gonamhonites 

 flanus to the Clitambonitina: may prove to be still more 

 remote than we had suspected. 



Dorsal interior. — Notothyrial cavity shallow or ob- 

 solete; notothyrial platform swollen and extended 

 laterally; chilidium and cardinal process protruding 

 above the interarea. Cardinal process thin, linear; 

 brachiophores orthoid, supported by lateral extensions 

 of the notothyrial platform (see pi. 8, fig. 7). Sockets 

 shallow. Adductor field subflabellate ; median ridge 

 obsolete or rudimentary. Subperipheral rim low. 



Geologic range. — Lower Ordovician (Canadian) 

 of Europe (Walchow (Bn) for G. -planus Pander). 



Species. — We offer here no list of species because 

 we had available for study very few forms of Gonam- 

 botntes. Of G. planus there was an abundance of 

 material, but we had no specimens of G. latus. We 

 had specimens of "G." inflexus and G. excavatus 

 Pander but these do not agree morphologically with 

 G. planus, from which our description was made up. 

 We will not re-assign Pander's species from his figures 

 or descriptions because both are rather inadequate and 

 mistakes would be inevitable. 



Discussion. — The old genus Gonamhonites has 

 been regarded by most writers as a synonym of 

 Clitamhonites and was so placed by Hall and Clarke 

 in 1892. Dall in 1877 listed G. lata, Pander's first 

 species, but never selected a type. Schuchert and 

 LeVene (1929), following Dall's lead, selected G. lata 

 as the type of the genus. A little later Opik (1930) 

 made a critical study and revision of the genus and 

 selected as the type G. planus Pander. Opik's selec- 

 tion unfortunately can not stand as Schuchert and 

 LeVene's choice has precedence. 



In the description of Gonamhonites presented above, 

 we have based our remarks on G. planus for two 

 reasons: (1) This is the only material we had avail- 

 able, G. latus being entirely lacking from the Schu- 

 chert Collection; and (2) Verneuil (Geology of 

 Russia) placed G. latus in the synonymy of G. planus. 

 It is a known fact that Verneuil took liberties with 

 Pander's work that would be unheard of to-day, and 

 it is very probable that some of the shells placed by 

 him under G. planus deserve recognition as indepen- 

 dent species. From Pander's figures of G. latus, there 

 is to us a strong superficial resemblance to G. inflexus, 

 a species that clearly is not a Gonamhonites. If it is 

 shown by subsequent workers that G. latus has affinities 

 with G. inflexus, a wholly different interpretation of 

 the genus will be required, and it may be found neces- 

 sary to set off G. planus as an independent generic 

 group on the basis of its unusual spondylium (pseudo- 

 spondylium) and non-perforated deltidium. 



In the absence of material, we feel obliged to follow 

 Verneuil's interpretation of G. latus as a probable 

 synonym of G. planus, although we feel strongly that 

 Verneuil as a rule took many liberties. On this basis 

 we are justified in regarding "G. planus" as a "cotype," 

 as it were. Therefore, as explained under Estlandia, 

 we were forced to make a new genus for shells differ- 

 ing very widely from Gonamhonites as described above. 



