232 
Limestone with Dinobolus transversus Salt. 
A piece of fine grained-crystalline limestone having become 
brownish-yellow through weathering and of about the size of a fist, 
contains a dorsal valve of Dinobolus transversus Salt. (1 p.59 pl. V 
fig. 1—6), which in spite of its extreme thinness has been preserved 
in admirable perfection. This boulder also, which was also found 
in the Tuinbouwstraat at Groningen, is a completely unknown 
species of erratics, as the fossil mentioned just now was not met 
with in any other country. 
The length of the valve is 3 cm, the largest breadth, across the 
centre, 4.2 cm. The almost straight hinge margin is 3.3 em. long. 
The dorsal valve is almost quite flat and reveals on its surface 
numerous, very faint, concentric lines of growth and an extremely 
fine radial striation. Whether there are“small spines ou the outer 
surface, as indicated by Davipson (le. pl. V, fig. 3 and 3a) cannot 
be made out. 
Of other fossils this boulder contains besides a number of detached 
portions of crinoid stems also a valve of Pholidops implcata Sow. 
(1 p. 80, pl. 8, fig. 13—17) and a valve of Beyrichia Jonesi Boll 
(13 p.-13, pl. I, fig. 10—12) and a pygidium of Proetus concinnus 
Dalm. (Pope lS 18rspan 4. pk, LV a fies, AOS ap Ane 
tig. 5). 
From all this it appears, therefore, that the block belongs to the 
upper Silurian, the zône being undetermined yet. 
Pholidops implicata Sow. contrary to Pholidops antigua Schloth. 
is probably quite unknown in our upper Silurian erratics as well 
as in those from Germany and Denmark, which is perhaps due 
to the fact that various authors have considered the two as synonyms 
(7 p. 96, 10 p. 173). It appears however, as Mosrre and GRÖNWALL 
(24 p. 30) have shown, that they were used for fossils which indeed 
are closely allied to each other but also form a distinct contrast. 
Only Krusow (6 p. 245) records that Pholidops implicata Sow. (= Crania 
wmplicata Sow.) is very abundant in West-Prussia in the boulders 
of the Upper-Silurian Beyrichia Limestone. I think however that 
he also refers here to Pholidops antiqua Schloth. 
In solid rock Pholidops implicata Sow. is known only from the 
island of Gotland (from the zÔnes c—h of Linpsrröm (12 p. 13). 
Muntue (27 p. 12—13) mentions the fossil from the layers 2—4 
distinguished by him and Van Horprn (25 p. 125) from y and es 
Linpstr6m, also, records the occurrence in Schonen (l.c. p. 26), but 
MoBerG and GrOnwALL state that the species there differs distinctly 
