Palceozoic Bioaloal Entomosfraca. 407 



specimen may have been about 1*5 millim. long. No descrip- 

 tions are given, but figs. 9 a, h, were supposed to be Beyrichia. 

 Klcedeni, and fig. 11 was referred to as a Beijvichia, with the 

 two little knobs more to one side than shown by the 

 drauffhtsraan. 



Placentula, gen. nov. 



Primitiu, pars, Jones & PIoU, Ann. & Mao-. Nat. Hist., March 1809, 

 p. 2:22. ' 



Valves suborbicular, nearly semicircular on the ventral 

 border, straight on the dorsal margin inside, but projecting 

 with unequal and variable angles at the outer dorsal region. 

 Surface flat or slightly convex, surrounded by a raised rim, 

 which slopes down suddenly outside to the edge of tlie valve. 

 This rim encloses a depressed and reticulated area, and in or 

 near the antero-dorsal region there is a small depression de- 

 fined by a raised loop-like border. Within certain bounds 

 all these features are variable in different individuals. 



The little loop looks like the curved ridge of Bollia pushed 

 away out of place, and in some cases is almost obsolete. 

 Though apparently near to the little Bolliceo^ figs. 13 and 14, 

 yet this form can scarcely belong to that genus, as the loop 

 touches and runs into the dorsal border ; and the general 

 shape is different. We do not now think that it finds its 

 right place in Pnmitia^ and prefer to regard it as distinct 

 under the new generic name of Placentula (Lat., a little 

 cake). 



r 



5. Placentula excavata, Jones and Holl. 

 (PI. XIII. figs. 10a, l{)b, 11, 12, and 16.) 



Primitia excavata, J. & H., Ann. & Mag. Nat. Hist, ser, 4, vol iii. 

 1869, p. 222, pi. XV. figs. 10 a, h, c. 



(Figs. 10, 11, 12: L. 11. H. 7. Th. 5. 

 Proportions:^ Fig. 16: . . . L. 15. H. 10. 



(^ Original specimen : L. 14. H. 9. Th. 6. 



These little bun-shaped carapaces often differ slightly from 

 the specimen first described and figured, the dorsal sulcus 

 being clearly defined by a narrow, raised, slightly oblique 

 loop ; and the raised marginal rim is more distinctly marked 

 in several individuals, but not more so in others. 



This is a variable species, individuals differing in size, 

 outline, relative convexity, the strength of the loop and of the 

 supramarginal border, and in the intensity of sculpture. 



28* 



