64 Prof. T. R. Jones on the 



Nat. Hist, October 1890, p. 323, pi. xl. fig. 6h). Possibly 

 tills species {ibid. figs. 5-8) should be separated from Entomis. 

 Fig. 8 a has a resemblance to the form distinguished by E. O. 

 Ulrlch as BarychiUna (Journ. Clnclnn. Soc. N. H. vol. xUi. 

 1891, p. 199, pi. xiii. figs. 1-4), which has longitudinal and 

 sinuous strige, with pitted interstices, unequal and thick 

 valves, without a mid-dorsal furrow, though Ulrich's fig. 2 a 

 seems to have a trace of it. E. variostriata in its younger 

 stages has the definite Entomidian sulcus, and, as other 

 species of this genus occasionally exchange the furrow for a 

 pit, it would not be necessary to make a separate genus on 

 that ground. The different style of ornament, however — 

 prickly ridges in one and meshed interstices in the other — 

 may be a reason, as well as the coarser growth of the valves. 



6ome of the Devonian ^/^tom/cZes appear to have had simple 

 and smooth strige (for instance, figs. 9 and 18, pi. xi., Ann. & 

 Mag. Nat. Hist. ser. 5, vol. iv. 1879) ; but E. serrato striata 

 had prickles along its costulai or raised strige (see page 321, 

 Ann. & Mag. Nat. Hist. ser. 6, vol. vi. 1890), indications of 

 which are little pits in the hollow casts or impressions 

 (intaglio) of the valves, and not filling the breadth of the 

 interspaces. E. variostriata, on the contrary, shows a square 

 mesh work (fig. 6 6, pi. xi., op. cit.), of relatively large 

 pattern, filling the space between the strige. 



Among the more or less modified specimens of E. serrato- 

 striata (Ann. & Mag. Nat. Hist. ser. o, vol. iv. 1879, p. 10+, 

 pi. xi.) fig. 9 shows the pit only ; in figs. 2 and 14 a faint 

 trace of the sulcus accompanies the central spot ; and in fig. 9 

 both are absent. The collocation, however, and general 

 mutual resemblance of the numerous specimens support the 

 idea that they are congeneric and specifically the same. 



In well-preserved specimens E. variostriata^ Clarke {ibid. 

 vol. vi. 1890, p. 323, pi. xi. fig. 8 a), has the pit instead of 

 the sulcus, whilst figs. 5-7 show the sulcus only. So also 

 in Primitia we may have — (1) the furrow, (2) furrow and pit, 

 (3) pit only. 



On account of the dlfterent style of ornament and the 

 coarser growth of the valves there is reason for making the 

 separate genus (^BarychiUna) ; and, even if it has no sulcus 

 at right angles with the hinge-line, but only a central pit, we 

 find that some allied genera have similar modifications. 



BarychiUna semen is from the Devonian Limestone with 

 Clymenia annulata, Miiuster, at Hadiberg, near Briinn, 

 Moravia. 



