Palceozoic Bivalved Entomostraca. 341 



(regarded by us as antero-ventral^ by Renter o.^ postero-ventral) 

 has pushed out and overhung the margin, thus altering the 

 shape of the valve. Take for instance the semicircular, fig. 14, 

 pi. V. (Ann. & Mag. Nat. Hist. ser. 2, vol. xvi. 1855) ; and 

 compare the regular figs. 5, 9, and 11, with the " big-lobed " 

 figs. 7 and 8 on that plate. We cannot therefore adopt 

 Mr. Renter's cleverly devised nomenclature [op. cit. pp. 630, 

 631) for the fore and aft furrows of the Beyrichian valves, 

 his " cephalic " and our " cephalic " being contradictory 

 terms. 



We have regarded the sulcus between the " sausage" and 

 " middle " lobes as equivalent to the nuchal notch of Crus- 

 tacea. Unfortunately there are no " ocular spots " in Bey- 

 richian valves to give a clue to the cephalic extremity. In 

 neither B. ocuUna nor B. oculifera^ Hall, is there any satis- 

 factory indication of this feature 5 nor has the exact position 

 of the muscle-spot been determined. We may note that 

 the Carboniferous, Devonian, and Lower-Silurian Beyrichke 

 did not take on the exaggerated lobe, so far as we are aware. 



Doubtless the alliances of the Leperditiad^*, whether amongst 

 themselves or with Ostracods on the one hand and Limnadiads 

 on the other, are not yet well understood, as their soft parts 

 are w^anting ; but, as all the living bivalved forms have the 

 ovary in the postero-dorsal region, it would be too strange for 

 this organ to be placed elsewhere in analogous fossil genera. 

 It does not seem possible to allocate satisfactorily the internal 

 organs to the external lobes ; and until we have all the Bey- 

 richioi before us, in their great multiplicity and in their suc- 

 cessional order, we cannot pretend to know all the features 

 and their probable biological meanings f. With regard to 

 the extraordinary outward growth of one lobe on each valve 

 in Beyrichia it might possibly have reference to a fully- 

 developed hepatic gland, if in this genus the liver had the 

 same position that it has in Gypris according to Zenker 

 (Archiv &c. 1854, vol. i. p. 37, pi. i. fig. 15). There is a 

 possibility of its having had a parasitic origin, like the 

 swelling caused by Bopyrics in the Prawn. The " big lobes " 

 are not always quite equal nor quite opposite on the two sides 

 in Beyrichioi. 



The protuberant and exaggerated antero-ventral lobe has 



* Month. Microsc. Journ. 1870, pp. 187 &c. 



t Some of the Cypridinadaj are smooth, but others have swellings of 

 the valves, which seem difficult to collocate with internal organs. Cypri- 

 della is " swollen here and there into tubercles, fewer in the young than 

 in the old state" (Monthly Microsc. Journ. vol. x. 1873, p. 74). 



