394 rnocKicDixas of rirr: natiosai. Mis/a'M. vouxxi. 



SUMMARY. 



I'^ifty-six spucioM. 'A \ ariotios. 



[iOwt'T ('amhriiiii, '2 8i)C'cios in oxtromo iippor part. 



Middhi (Cambrian, 2(5 spocics. 



irjjprr Cambrian, 1!) Kp(^(rit's and li xarictiiis. 



Onlovician (LovviM"), 11.' HpocicH. 



I'assin;;' from Lower to Middlo Cainbriiin, '2 sjxicies in ])aHS!ij:;o bcjds. 



rassiiifi IVoMi Middi(* to Upper (Cambrian, 2 Hpocjics. 



I'aHHini;' from np])<ir Oanibriaii to l)aHo of ()r(b)vician, '2 spocics. 



Subgenus LINGULELLA Salter. 



(i'lato WVII. li.i-H. i-n.) 



lAtKjiiUUd SAi/noi!, Mem. (itiol. Surv. (Jt. Brit., IHtitJ, III, p. H.S:?.— Davidson, Brit. 

 FoHS. Uracil.. Silnr. Hracli., lS(!(i, I't. 7. p. T)").— Wauiott, 18H(i. Mull. U. S. (Ji'ol. 

 Siiiv., No. :$(), i)p. !»r)-!»8; 'IVnth Ann. b'ept. U. S. Gool. Surv., 18!)1, pp. (i()7- 

 (iOS, pi. i.w II. — llAij. and (!i,akkk (pars), 1S92, I'al. Now York, Vlil, I't. 1, 

 Pl». .^>r>-.")!), 1(>:{, ])!, II, lijfH. T>-V,\\ Klcvonth Ann. KN-pt. Nc^w Yorl< State (Jool., 

 IXilj, ]), 2H2, lijjjnros in toxt only. 



/)i(i;in()sis. — Slu'll siilMM|iiiviilvc, c(|uihiteral; olongato-ovate, broad 

 oviilc, or siil)triiiiiji;uliir in outline. V^enti'al or i)(Hli(;le valve usually 

 subiHMiiiiiiiiito, with a distinct cardiniil aroa, i)e(licle j^roove, ami llcxuro 

 liiK's. Dorsiil or bracliiiil valve soiucwliat the shorter, less acumiiiate, 

 and with a less clearly marked i)e(li<'.Ie {groove on the shorter cardinal 

 area. Surface of slicll marked by line concentric stria' and Hues of 

 urowMi, and in soim^ species finely inosetdjiting aud lamellose stria', 

 also, in most if not- all species, radiating" stria'. 



Muscular impressions usually iudistiiutlly preserved. In the ventral 

 valvt^ what. a])i)ears t(» be a divided umbonal scar has been observed in 

 (>. (/..) (lorisi (Plate XW'II, (i^-. ."{,</) and (>. (h.) ocHhniniiliix (Plate 

 XXVllI, \\g. 1,//) .\ faint trace of a pedicle scar was found in the 

 latter specimen on the shallow oroovo between the umbonal scars at wi, 

 Plate XXVIII, lig-. 1. Its position is also imlicated on Plate XXVII, 

 lij?. 3, at )n. The anterior and concrete laterals aie well shown in (). 

 (/y.) (((mtauijulKK (Plate XXVI II, lig 1, / and c), but they have iu)t been 

 seen in (). {L.) tlarisi exce])t doubtfully, as show'n by c, Plate XXVU, 

 fij;'. 1. The muscular scars of the dorsal (brachial) valv(^ are (luite satis- 

 factorily preserved in several si)ecies of the jnenus. The central scars 

 (//, Plati^ XXVIl, tig. 1) of (>. (/a) <larifii are clearly delined in a speci- 

 men from I'oit Madoc, and the small anterior laterals and outside 

 laterals are also well shown in the stime specimen. In (). (/>,) anii>li<s 

 (Plat(^ XX\'1I1, lio. I) the centrals occur in the same relative position 

 as in (). (/y.) (larisi, but they are much smaller, while in O. {L.) arti- 

 tdiifliiliis {\i<x. L*) they are situated much farther forward and are only a 

 litth^ longer than in (). {L.) (iniiihis. The anterior laterals of (). (/>.) 

 (larisi (/, Plate XX VII, liii. I) are situated close to the anterior end of 

 a median rid. ue, while in (>. (/>.) <(cut(()itiiili(n they are a short distance 

 away from the median ridye and much farther forward than in (). {L.) 



