306 MOLLUSCOIDEA—BRACHIOPODA . SUB-KINGDOM V 
Elkania, Ford (Billingsia, Ford). Like Obolella, but with a small platform 
in the dorsal shell. North America. 
Obolus, Eichwald (Ungula, Pander ; Ungulites, Bronn ; Aulonotreta, Kutorga ; 
Acritis, Schmidtia, Volborth), (Fig. 506). Much like Obolella externally, but 
larger and with more prominent cardinal areas in both valves, Ventral valve 
with a median septum extending to about the centre of the valve. 0. Appolinis, 
Eichwald, occurs in vast numbers in the Unguliten-Sandstein of Russia. 
Neobolus, Waagen ; India. otsfordia, Matthew ; New Brunswick. Spondyl- 
obolus, M‘Coy (Fig. 507). Treland. 
Family 3. Trimerellidae. Davidson and King. 
Large, thick-shelled, inequivalved Obolacea, with the ventral cardinal area usually 
very prominent, triangular, and tranversely striated. Adjustor and anterior adductor 
muscles elevated upon solid or excavated platforms. Cambrian to Silurian. 
Dinobolus, Hall (Conradia, Hall; Odolellina, Billings). Cardinal area not so 
prominent as in the other genera of this family. Platform small, with abruptly 
conical vaults. Ordovician and Silurian; North America, Great Britain, 
Bohemia, Gottland, and Esthonia. 
Monomerella, Billings. Similar to 7rimerella, with well-developed platforms 
D 

Fic. 508, 
Trimerella Lindstroemi, Dall sp. Silurian; Gottland. x 1/9. A, Shell seen from the dorsal side. B, C, In- 
terior of dorsal and ventral valves, respectively. D, Cast. (4 and B after Davidson; Cand D after Lindstrom.) 
in both valves; that of the dorsal valve, however, but slightly excavated. 
Silurian ; North America, Gottland, and Livonia. 
Trimerella, Billings (Gotlandia, Dall), (Fig. 508). Platforms long, narrow, 
well-developed, and doubly vaulted. Dorsal beak often thickened into a 
prominent apophysis extending against the cardinal slope of the ventral valve. 
Silurian ; North America, Gottland, and Faro. 
Lhinobolus, Hall. Silurian; North America. (?) Lahkmina, Oehlert (David- 
sonella, Waagen). Lower Cambrian ; India. 
Superfamily 2. LINGULACEA. Waagen. 
Elongate, thin-shelled, burrowing, derived .Atremata, with a more or less long, 
worm-like, tubular, flexible pedicle. Cambrian to Recent. 
Family 1. Lingulellidae. Schuchert. 
Spatulate, inequivalved Lingulacea, structurally intermediate between the Obolidae 
and Lingulidae. Cambrian and Ordovician. 
