302 CAMBEIAN BRACHIOPODA. 



The presence of spines in inarticulate genera is of rare occurrence. The oldest known 

 indication of their presence in other families than the Paterinidse is on Bicia gemma (PL L, fig. la) 

 and Nisusia festinata (PI. C, fig. 1 ) of the Lower Cambrian. The Middle Cambrian Nisusia 

 alberta (PI. C, fig. 3c) has a series of strong spines, and, in the Upper Cambrian, Acrotreta spinosa 

 (PL LXXIX, figs. 4a, 4b, and 4g), Schizamhon (PL LXXXIV, figs. Id and 3a), and HelTuersenia 

 ladogensis (PL LXIII, fig. 7e) appear to have had a spinose surface. 



NEOTBEMATA. 



OholeUa (Pis. LIV and LV) has, so far as known to me, only concentric lines and ridges of 

 growth, but the surface of Botsfordia is usually quite ornate. The granular type is best shown 

 by B. granulata (PL LVII, fig. 4r) and B. cselata (PL LIX, figs. Ih and lo), and the pitted or 

 reticulated type, formed by the crossing of obliquely concentric ridges, by B. pulcTira (PL LXII, 

 figs. 5, 5a-f, and 5k). Botsfordia? iarrandei (PL LVII, figs. 7, 7a, and 7b) appears to have 

 a smooth surface or one marked only by concentric growth lines. 



Trernatobolus of the Siphonotretidse is like OholeUa in having a plain surface, but in YorJcia 

 orientalis (PL LXXXII, fig. 3a) the surface is of the reticulated tj^pe and resembles that of 

 Micromitra {Iphidella) pannula of the Atremata. SipJionotreta has a finely granulated surface 

 (PL LXXXI, figs. 6 and 6a), also a pustulose surface (PL LXXXI, figs. 5 and 5a). The latter 

 type is found in the Atremata in Mickwitzia (PL VI, fig. 2) and the granulated surface is present 

 in Botsfordia (PL LVII, fig. 4r) of the ObolellidEe. The surface of Schizamhon (PL LXXXIV, 

 figs. Id and 3a) differs from all other genera of the Neotremata exceut Acrotreta (PL LXXIX. 

 fig. 4g) in being spinose. 



The surface of Acrotliele varies in almost the same manner as that of Micromitra. Species 

 occur with only concentric growth lines, as in Acrotliele suhsidua (PL LX, figs. Ic, Id, and li), 

 or the same species may have a few radiating ridges (PL LX, figs, la, lb, and 8). The radiating 

 ridges may be characteristic of some forms of the adult shells of the species, as in ^. matthewi 

 multicostata (PL LXI, figs. 5, 5a-c). In addition to these, there may be an irregvilar more or less 

 inosculating series of fine concentric ridges, as in A. avia (PL LXII, fig. Ij); a finely granular 

 surface, as in A. coriacea (PL LVI, fig. Ig) ; a more distinctly and strongly granular surface, as in 

 A. {Bedlichella) granulata (PL LVI, fig. 2g) or A. prima costata (PL LXI, fig. 4d). A pitted 

 surface is sometimes formed by the crossing of obliquely concentric narrow ridges, as in ^. &eZZa- 

 punctata (PL LVII, fig. 3b). 



Only a few species of Acrotreta have more than the smooth surface with concentric lines. 



I was greatly surprised when I found a shell shomng a spinose surface, A. spinosa (PL LXXIX, 



figs. 4a, 4b, and 4g), and again when I found a reticulated surface, A J cancellaia (PL LXXIX, 



fig. 5a). Both species are from the fauna of the Cordilleran sea; A. spinosa developed in late 



Cambrian time and AJ canceUata in early Ordovician time. The closely related genus 



AcrotJiyra has a very fine Westonia type of surface (PL XLVII) that can be seen only with the 



aid of a strong lens. 



PBOTREMATA. 



The ornamentation of the surface of the sheUs of Protremata is usually in the form of 

 radiating striae, lines, and ridges of varjnng size and number, with concentric lines and ridges 

 of growth. The radiating striae, lines, and incipient ridges or plications are usually first seen on 

 the inner laminations of the shell, and often this occurs in species that do not show it on the 

 outer surface of the shell. This is beautifully shown in the atrematous genera Mickwitzia 

 (PL VI, figs. Ik and 1 1), Oholus (PL VIII, figs, li and 2; PL X, figs. 2 and 2e), Oholus {Westonia) 

 (PL XII, figs. 7 and 7c; PL XLVII, figs, la, Ig, and Im), Oholus (JLinguloholus) (PL XVI, figs. 1, 

 lb, 2c, 2f, 2h, and 2i), Lingulella (PL XVII, fig.ll; PL XXXI, figs. 6e and 6g; PL XXXVIII, 

 figs. 2d and 2f), Lingulella {Lingulepis) (PL XLI, figs, la-c, If-h, and Ij-m), and Dicellomus 

 (PL LII, figs. 2c and 2h; PL LIII, figs, lb, Ic, 2, 2a, 4a, 4d, and 4e). In Bicia gemma (PL L) the 

 radiating lines and ridges occur on both the interior and exterior surfaces, and there are also 

 elongated tubercles that suggest fine spines. In Kutgrgina granulata (PL V, figs. 5b and 5c) 



