OBOLID^. ' 473 



Cambrian time represented by the fauna at Troy, New York. It is to be borne in mind that 

 the fauna at Troy was collected both from stratified and conglomerate limestones. On this 

 account it is not practicable to state that all the species from either are from the same geologic 

 horizon, but LinguMla schucherti (Walcott) (PI. XXI) and Oholella crassa (Hall) (PI. LIV) 

 occur in the same pieces of limestone. Lingulella granvillensis Walcott (PI. XXII) occurs at 

 numerous places in Wasliington County, New York, in strata near the top of the Lower Cambrian 

 zone. Lingulella naihorsti Linnarsson (PI. XXXI, figs. 1, la-b) occurs in the Holmia hjerulfi zone 

 of Sweden. It has nearly the outline of Lingulella acutangula (Roemer) in some examples of 

 the ventral valve. (Compare PI. XXXI, fig. Ic, with PI. XVII, fig. la; and PI. XXXI, fig. 

 la, with PI. XVII, figs. Ih-k; also fig. 1 on each of the two plates.) Lingulella delgadoi Walcott 

 (PL XXIX, figs. 6 and 6a) from the Olenellus zone of Portugal is, from our present knowledge 

 of it, a true Lingulella. 



Matthew [1903, p. 109] in speaking of the growth of Lingulella and allied forms, speaks of 

 a law that the young shells are. often round and the adults more elongate. This is in accord 

 with the view that the protegulum of all forms of the Atremata is semicircular or semielliptical. 

 In Lingulella (Lingulepis) gregwa (Matthew) (PI. XLIV) and L. (L.) exigua (Matthew) (PI. 

 XLIII) the young shells are more elongate than the adult, owing to the broadening of the 

 anterior portions of the valves as they increase in size. 



Lingulella? paliformis [Hall and Clarke, 1892c, PI. II, figs. 6-8] has the form of some of 

 the more acuminate species of Lingulella, but from a study of the tj^pe specimens I am led to 

 conclude that the material is too limited to decide the true generic relations of the species. 

 The area of the dorsal valve is like that of Lingulella, but the only specimen showing the area 

 of the ventral valve suggests that the pedicle furrow was confined to the dorsal valve. Nothing 

 is known of the interior marldngs of either valve. 



The vertical range of Lingulella is from the upper horizon of the Olenellus or Lower Cambrian 

 fauna to the summit of the Cambrian and into the Ordovician fauna. One of the oldest known 

 species is Lingulella schucJierti (Walcott), found in the limestone conglomerate at Troy, New 

 York, in association with Oholella crassa (Hall), Bicia gemma (Billings), Elliptocephala asa- 

 plioides Emmons, etc. Lingulella granvillensis Walcott, which is associated with Olenellus 

 in the strata referred to the upper portion of the Olenellus zone, L. naihorsti Linnarsson of the 

 Holmia Tcjerulfi zone of Sweden, and L. delgadoi Walcott are found in association ^iih. Olenellus. 

 The greatest development of the species is in the Middle and Upper Cambrian, only a few forms 

 continuing on into the Lower Ordovician. 



The small Lingulella desiderata ranges from the base of the Mddle Cambrian in the Cor- 

 dilleran region to the Ordovician. Thei-e may be specific differences, but in the large amount 

 of material now available for study there are none that appear to be of specific importance. 

 Lingulella isse also has a great vertical range. 



Lingula attenuata Sowerby [Davidson, 1866, p. 44, PL III, figs. 18-27] has the form of Lin- 

 gulella and may possibly be a survival into the Middle Ordovician of a species of the genus. We 

 do not have sufficient data to know whether the interior markings of the valves are more like 

 those of Lingula or Lingulella. 



Of the 77 sjiecies and 4 varieties fi'om the Cambrian referred to Lingulella in this monograph, 

 5 species occur in the Lower Cambrian, 46 species and 1 variety in the Middle Cambrian, 35 

 species and 3 varieties in the Upper Cambrian, 6 species in the passage beds between the Cam- 

 brian and the Ordovician, and there are 13 species from the Ordovician. Of the Middle Cam- 

 brian species 13 pass up into the Upper Cambrian, of which two are found in the Ordovician. Two 

 species pass from the Upper Cambrian to the Ordovician and two from the Upper Cambrian 

 to the passage beds. 



The range of all known species is given in the tables of genera and species (pp. 98-113). 



Subgenera of Lingulella. — Leptemholon Mckwitz [1896, p. 199] is rather difficult to charac- 

 terize. Mickwitz [1896, p. 199] says of it: 



The subgenus Leptemholon is based on a species of Obolus which externally resembles Lingula very closely, and 

 in fact was regarded as such by earlier authors [Schmidt, Fr., 1881, p. 17]. The specimens of the internal surfaces 



