318 CAMBRIAN BRACHIOPODA. 



and is the oldest brachiopod known from the Atlantic Province. Bicia (PI. L), OboleUa (Pis. 

 LIV and LV), Quebecia (PI. CIV), Botsfordia cselata (PL LIX), Acrothele hellapunctata (PI. LVII, 

 figs. 3, 3a-b), A. decipiens (PI. LVIII, figs. 3, 3a-d), A. woodwortM (PI. LX, fig. 6), Acrotreta 

 emmonsi (PI. LXV, fig. 6), ^. primseva (PI. LXIX, figs. 1, la-f), and Yorlcia (PI. LXXXII) occur 

 with other forms in the upper portion of the Lower Cambrian fauna. All of these examples of 

 inarticulates indicate that the brachiopod fauna had advanced far in its evolution in Lower 

 Cambrian time. Among the progenitors of the Protremata, Kutorgina (PL V) occurs in the 

 Mesonacidse fauna, and Schuchertina (PL LI) of the Middle Cambrian probably springs from 

 the Kutorgina stock in Lower Cambrian time. Among the articulates we find, of the order 

 Protremata in the Lower Cambrian, several species ol Billing sella (Pis. LXXXVI-LXXXIX), 

 Nisusia (Pis. C and CI), and Swantonia (PL CIV), all from the upper zone of the Mesonacidse 

 fauna. (See lists of genera and species, pp. 98-109.) 



ATREMATA. 



The most primitive form of the Atremata known to me is Bustella edsoni (PL I, figs. 1, la-e) 

 of the upper portion of the Lower Cambrian terrane. It is without a false cardinal area, and 

 there is only a sUght indication of a pedicle furrow; some of the less well-preserved shells suggest 

 the protegulum stage of the Bracliiopoda. Mickwitzia (PL VI, figs. 1" and 3), Helmersenia (PL 

 LXIII, figs. 7b and 7d), and VoTborthia (PL I, figs. 6 and 6e) have an obscurely defhaed false 

 cardinal area on the ventral valve. In Helmersenia the pedicle opening is produced by the 

 gaping of the valves; in Volbortnia (fig. 33, p. 366) it is produced by the bulging of the cardinal 

 margins. In Micromitra (Pis. II, III, and IV) the posterior margins of the valves may be 

 nearly closed as in' if. pealei (PL III, figs. 3b and 3e'), or have a more or less open delthyrium 

 as in Jf. (Iphidella) pannula (PL IV, figs. Id, If, 2a", 2b', 4a', and 4d'). In Curticia (PL I, 

 figs. 2', 2b, 2a", and 2d) the open delthyrium is more developed than in Micromitra, although 

 the cardinal area is not outlined. Curticia appears to be a form intermediate in character 

 between Micromitra of the Paterinidse and Oholus of the OboUdss. It shows no trace of a pseu- 

 dodeltidium or any closing of the delthyrium by an extension of the area across it. In the 

 graphic systematic scheme (p. 317) it is placed as a family descendant from Oholus. 



In the diagram on page 317 the lines of descent of the various genera are grapliically out- 

 fined, but our information is often so fragmentary that the scheme is necessarily imperfect. In 

 this the Bustella type of the upper Lower Cambrian is assumed as the known form that most 

 nearly approaches the protegulum stage or the first stage in Avhich it would be possible to have a 

 brachiopod preserved as a fossil. From the pre-i?usteZZa radicle Micromitra developed in early 

 Cambrian time and continued nearly to the close of the Upper Cambrian, giving rise in the 

 Lower Cambrian to MicTcwitzia and in the Upper Cambrian to Helmersenia and Volhorthia. 



Oholus, branching from the Rustella protegulum radicle, is first known in the Lower Cam- 

 b'ian a little later than Micromitra. It persisted on into the Ordovician, giving rise in early 

 Middle Cambrian time to its subgenera Palaeoholus and Westonia, in late Middle Cambrian time to 

 Fordinia and to 0. (Acritis?) rugatus. Other subgenera, Schmidtia, Broggeria, and Miclcwitzella, 

 appeared in late Upper Cambrian or early Ordovician time. Bicia is taken from the 'pre-Oiolus 

 radicle. Dicellomus appears in central ]\'Iiddle Cambrian strata and continues into the Upper 

 Cambrian. It probably originated in the Bicia phyllum in Lower Cambrian time. ETkania 

 begins in central Middle Cambrian strata and continues well into the Upper Cambrian. It 

 appears to have been an offshoot from Oholus without known direct descendants. Neoholus, 

 with its pecuhar platforms pointing to the future Trimerellidse, is probably a descendant from 

 sonre Lower Cambrian foi'm that branched off from Oholus. The descendants of Neoholus, if 

 such existed, are unlaiown in the late Middle and LTpper Cambrian. Curticia is given as an 

 ofl^shoot from Oholus in Upper Cambrian time and Linguloholus in the Lower Ordovician. 

 Fordinia appears to have been an offshoot from Oholus in Middle Cambrian time and to have 

 disappeared without descendants. 



