some Silurian Leperditiee. 169 



to tlie * Wisby group ' (so termed by Lindstrom and myself) ; 

 and it is very often found near Wisl)y and in the neighbour- 

 ing localities on the north-west coast, as well-preserved perfect 

 (bivalve) specimens. L. halthica occurs only in the Middle- 

 Gothland stage, and principally on the east coast, near Faro 

 and Hlite. It is not rare, but the valves always occur separate. 



" In Norway both species are met with on the island of 

 Malmij (I Avas there in 1875), in the Bay of Christiania ; but 

 L. Hisingei'i is found only on the east coast of that island, 

 in limestones corresponding to the ' Wisby group ' of (J otli- 

 land ; whilst L. haltldca is found on the west coast in strata 

 \fii\\ Pentamerus ohlongus (Kjerulf's ' Stage VI.'), correspon- 

 ding to the Middle-Gothland stage. 



" With us, in the Baltic Provinces of Russia, L. Hisim/eri 

 is found also in the lowest stage of the Upper Silurian (my 

 zone G). The form shown in fig. 22 {L. Hisingeri^ var., 

 Schmidt) of my memoir, there termed a variety of L. Hisin- 

 geri, belongs to the stage H (with Peatamerus oblongus or 

 esthonus)^ and may now be better named L. halthica^ var. 

 contracta, Jones, as it seems to be identical with your variety 

 contracia (Ann. & Mag. Nat. Hist., Nov. 1881, p. 337) ; and, 

 moreover, some traces of the transverse striation are visible 

 on the inverted ventral plate of the left valve. The typical 

 L. haltJiica does not occur with us ; but it is often met with 

 in the erratic Silurian boulders of Northern Germany. 



" 2. Another point I have to object to is about L. grandis, 

 Schrenck {L. giganiea^ F. Komer). You believe"^' that Bar- 

 rande is right in calling it an Isochilina^ notwithstanding that 

 in establishing that genus you pointed out that tlie carapace 

 is equivalve^ the margins of the valves meet'ini^ tinifbrjjili/j and 

 not overlapping as in Leperditia. I figured two right valves 

 in my figs. 5 and 6, and two left valves in figs. 3 and 4 ; and 

 you can see there the inverted plate on the ventral border 

 of the left valve in fig. 3 a, and the striking difference be- 

 ween the two valves wlien comparing the ventral borders of 

 the left and the right valve in figs. 3 a and 5 a. The right 

 valve must have been overlapping. The difference in that 

 aspect between our species and other Leperditioi consists 

 merely in the inverted plate of the left valve occupying only 

 a middle part of the ventral border, and not the whole of it. 

 L. grandis could thus be, perhaps, the type of a new subgenus, 

 but by no means an Isochilina. The external outline of tlic 

 valves is very constant ; and I cannot see any varieties in that 

 respect. Nor can I agree witli you in uniting your large 

 specimen from llupcrt's Land to our species. Your form 

 * Auu. & Mag. Nat. ffist. Nov 1881, p. 347. 



