OBOLIDiE. 469 



Lingulella Hall and Clarke (in part), 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 55-59. (Original 

 description copied and genus discussed. Lingulella davisi is given as the type, but figures of Obolus {Westonia) 

 ella accompany the text and as a generic illustration Botsfordia cxlata is figured on PI. II. Species belonging 

 with other genera are also mentioned as belonging to Lingulella.) 



Obolus (Euoholus) Mickwitz (in part), 1896, Mem. Acad. imp. sci. St.-Petersbourg, Sth ser., vol. 4, No. 2, p. 129. 

 (Described in German.) 



Obolus (Lingulella) (Salter), Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 390-392. (Discussed.) 



Lingulella Salter, Matthew, 1899, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 3, No. 18, p. 201. (Characterized 

 in discussion of Palseobolus, see p. 471, for copy.) 



Obolus {Lingulella) (Salter), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 683. (Characterized.) 



Eoobolus Matthew, 1902, Trans. Roy. Soc. Canada for 1902, 2d ser., vol. 8, sec. 4, No. 3, p. 97. (Characterized without 

 reference to Mickwitz and without any indication of the fact of its being intended as a new subgenus; see 

 Matthew, 1903, p. 135.) 



Lingulella Salter, Matthew, 1902, idem, p. 103. (Nova Scotia representatives mentioned.) 



Leptobolus Matthew [not Hall], 1903, Geol. Survey Canada, Kept. Cambrian Rocks Cape Breton, pp. 105-106. 

 (Described, see p. 472 for copy.) 



Lingulella Salter, Matthew, 1903, idem, p. 116. (Discussed.) 



Obolus (Eoobolus) Matthew, 1903, idem, p. 135. (Characterized as a new subgenus.) 



Lingulella Salter, Delgado, 1904, Communicagoes Commissao Servigo Geol. Portugal, tome 5, fasc. 2, p. 367. (Dis- 

 cussed in French.) 



'Mot Lingulella Grab Av a.nd Shimer, 1907, North American Index Fossils, voL.l, p. 192. (Described, but one of the 

 species referred to belongs with Obolus (Westonia) and the other is the type of that subgenus.) 



Lingulella Salter, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 144. (Classification 

 of genus.) ' 



Type of genus. — Lingula davisi McCoy. 



Valves subequal, equilateral; elongate ovate, broad ovate, or subtriangular in outline. 

 Ventral valve usually subacuminate, wdth a distinct area, pedicle groove, and flexure lines. 

 Dorsal valve sonaewhat shorter, less acuminate, and with a less clearly marked pedicle groove 

 on the shorter area. Beaks terminate at the margin of the areas, which are usually in the 

 plane of the margins of the valves; the areas, which vary in size and shape in the different 

 species, are usually more or less triangular; in the ventral valve they may be so shortened and 

 arched as to nearly lose this marked form; the areas of the dorsal valve also vary in their form 

 length, and extension on the cardinal slopes. 



Shell substance calcareocorneous; structure consists of a thin outer surface layer and 

 numerous inner layers or lamellse that are subparallel to the surface over the posterior portions 

 of the shell and more or less obUque to it over the central, lateral, and anterior portions; the 

 short oblique layers usually form the inner flattened rim of the valves which is frequently seen 

 in the casts (PL XVII, fig. li). Surface of shell marked by fine concentric striae and lines of 

 growth, and in some species finely mosculatiag, lamellose strise; also, in most if not all species, 

 radiating strise and lines . 



The visceral area (splanchnocoele [Mickwitz, 1896]) is usualh^ confined to the central and 

 posterior portions of the ventral valve, but it may extend far into the brachial area (brachio- 

 ccele [Mickwitz, 1896]) (PL XVII, fig. Ic); in the dorsal valve it extends farther forward than 

 in the ventral valve of the same species; in both valves it may range from the posterior third 

 of the shell forward to the anterior third, and in the dorsal well into the latter; in both valves 

 the visceral area extends back to the base of the areas where it is bounded exteriorly by the 

 flexure lines (lines of folding of the area lamellp')- 



A narrow median ridge or septum is frequently observable in the dorsal valve, but with the 

 exception of what may be considered as indicating its probable presence in one specimen of a 

 ventral valve of Lingulella. davisi (McCoy) (PL XXXI, fig. 6f), no traces of a septum have been 

 observed in the ventral valve of any of the species that I have studied. The main vascular 

 sinuses vary in size, direction, and length in the various species; in all they begin in front of 

 the area at the median hne and extend forward and outward across the parietal band into the 

 central-lateral and anterior parts of the brachiocoele. The impressions of the secondary vascular 

 canals are rareh^ preserved, but the few traces observed indicate that they were numerous and 

 extended toward the peripheral canal and into the middle of the shell in the direction neces- 

 sitated by the arrangement of the main sinuses and the boundaries of the visceral area. 



