30 Transactions of the Society. 



average measurement is much the same as in L. anatina, for which 



Gratiolet gives ■ 0008 mm. 



On the other hand, a marked difference of detailed structure 

 is seen in L. anatina : firstly, in the general predominance, as 

 Gratiolet points out, of the shelly layer ; and, secondly, in the 

 non-structureless appearance of the horny layers, which are in this 

 section composed of parallel fibres of a transparent character. 



The Nature of the Shell structure in a Fossil (Silurian) exam///' 

 of Lingula. — Considering the immense age of this fossil,* it is 

 surprising to find the shell retaining so much of its original struc- 

 ture, not only physical but chemical. In regard to the latter 

 point, the shell, when tested, gave a decided reaction for phosphoric 

 acid.t The structural details of this fossil shell shows the calcific 

 and horny layers to be in about equal proportional thickness. It 

 is therefore about as corneous as in L. anatina, and decidedly more 

 shelly than in L. alhida. The layers are slightly flexuose, and 

 tend to separate between the horny layers. Occasionally the 

 vertical tubes passing through the calcific layers have been pre- 

 served, and they are seen to be rather larger than those of either 

 recent species quoted, measuring ■ 0026 mm. in diameter. This 

 entirely bears out the statement by Hall and Clark,:}: who remark 

 on the comparatively large pores in the shell of a Lingula from 

 the Waverly Sandstone (Lower Carboniferous) of Ohio, and suggest 

 therefrom, " That these vertical canals have sometimes attained a 

 greater development in the extinct than in the living species." In 

 the present examples of L. lewisii var. flemingtonensis, the shells 

 are of a purplish-brown colour, and still show a chill horny texture 

 like that of polished cow-horn, and under a tolerably high power 

 is seen to be finely-punctate. This Australian Silurian example of 

 the genus appears to be the oldest known Lingula, which still 

 retains much of its original structure. Flakes taken from the 

 horny layers show a vermiculated tubulated structure nearly 

 identical with Carpenter's figure, but of a more irregular character. 

 As in Carpenter's example, these canaliculi are set obliquely to 

 the lamina: and tend to branch. 



Summaky. 



1. The shell-structure of the living Lingulse, as shown by the 

 two species examined, are very diverse in their detailed characters, 

 the horny layers being predominant in one, the calcareous in the 



other. 



2. In Lingula (Glottldia) alhida the horny laminae are canali- 



* Lingula lewisii J. de Sowerby, var. flemingtonensis Chapman, from the 

 Silurian (Melboumian stage) of Flemington, near Melbourne. 

 t Chapman, loc. cit., p 183. 

 % Pal. New York, viii. (1892) Pal. Braoh., pt. 1, p. 17. 



