PalcBozoic Bivaloed Eatomostraca. 349 



it is noticed also by Kolmodin (QEfvers. K. Vet.-Akad. 

 Forhandl. for 1879, vol. xxxvi. 1880, p. 137. 



We must remember that by themselves neither the splitting- 

 up of the lobes nor the granulation of the surface can be taken 

 as specific characters, so many instances of the capricious 

 adoption of these features being known. 



(1) BeyricMa tuherculata, var. qihhosa^ Renter. 

 {PL XII. figs, la, l'^*.) 



Proportions*: — Length 27. Height 16. Thickness 18. 



In one specimen, seeming to belong at first sight to the 

 varietal group of B. Klmdeni-torosa (see further on), the sub- 

 division of the gigot-lobe has proceeded a step further, and 

 there are three lobules, thus presenting a leading character of 

 B. tuherculata^ Kloden. The other lobe is distended ventrally. 

 This individual is scarcely to be distinguished from the 

 variety figured and described by G. Renter as B. tuhercidata- 

 gihhosa (Z. d. d. g. G. 1885, p. 634, pi. xxv. fig. 2 s). 

 Krause's fig. 12 h, pi. i. (Z. d. d. g. G. 1877, p. 30), B. twher- 

 eiilafa, is very similar. 



This specimen (on slide no, 9 of Mr, J, Smith's collection) 

 is from the Upper-Silurian beds at Dudley Castle, 



The same collection has a modification of B. Kloedent, var. 

 , suhtorosa, which imitates a variety of B. tuherculata (see 

 p, 353, under var. suhtorosa). 



2. BeyricMa Klcedeni, M'Coy, 1846. 



Some observations on this variable species, as to its 

 history, character, and synonyms, were offered by one of us 

 in the Ann. & Mag, Nat. Plist. ser, 2, vol. xvi. 1855, pp. 166 

 et scq., and in the Geol. Mag. dec. ii, vol. viii. 1881, p. 345. 



The typical form .is characterized by the nearly semicir- 

 cular or ovate-oblong shape of the valves and their three neat 

 lobes. The front and hind lobes are large, nearly equal, pyri- 

 form and curved ; and the hind lobe turns up sharply from 

 below towards, and often joining, the smaller oval midlobe. 

 The surface may be granulate or smooth, and the ventral 

 margin more or less developed. Sometimes the anterior and 

 the posterior lobe each turn towards and meet the midlobe, 

 with distinct necks of junction ; and, when so connected, all 

 become more or less attenuate and straight (vars. intermedia^ 

 pauperata). Sometimes the front and hind lobes run together 

 below, leaving the midlobe distinct and either free or lying 

 against the inner side of one of the other lobes (var. tuhercu- 

 lata). On the other hand the front and hind lobes become 



* If divided by 15, these will give the measurements in millimetres 

 and parts of a mi)limetre. 



Ann. & Mag. N. Hist. Ser. 5. To?, xvii. 24 



