22 NON-MARINE MOLLUSCS OF SURINAM. 
Coast of Surinam. ten Kate. 
Environs of Paramaribo. van Heurn, 1911. 
Coronie. van Heurn, 1914. 
Drouet 1859, p. 76. Rivers and ditches in Surinam. 
Martens, 1873, p. 195. Surinam. 
At first I felt inclined to classify the great number of 
specimens, collected by Mr. van Heurn, in two or three 
different species. There are some very large specimens, 
having a longest diameter of 30 m.M. and more (one 
specimen 34m.M.), which, when not found together with 
the other ones, I would be inclined to consider as P. oliva- 
ceus. When comparing them however with true P. olivaceus, 
they appear to have the base much less funnel-shaped and 
the last whorl less compressed; moreover this whorl, viewed 
from the basal side, does not surpass so much in width the 
preceding as in P. olivaceus. The majority of the shells 
has a longest diam. of 17 à 20 m.M., and possesses about 
6 whorls. These ones are connected by intermediate forms 
with the large specimens having about 7'/, whorls, and also 
with very small, immature ones of about 4 whorls. After 
having carefully compared the corresponding whorls in the 
whole series, I failed to find sufficient grounds for separa- 
ting the large and the smaller specimens. A very distinct 
feature is the deeply funnel-shaped upper side, and the 
rather plain basal side, the latter having only a shallow 
funnel in the centre. The last whorl of the larger specimens 
has its greatest width above the periphery. 
Possibly the average specimens of this species have a 
longest diam. of about 18 m.M. and 6 whorls, and only 
under very favorable circumstances they are forming 1 a 
1'/, whorl more, and are reaching the size of P. olivaceus 
and P. cumingianus Dkr. By no means being willing to 
doubt the occurrence in Surinam of P. olivaceus, I only 
will suppose the possibility that the large specimens of 
P. guadelupensis have been mistaken for it. 
* 53. PLANORBIS LUGUBRIS Wagn. 
Planorbis lugubris, Wagner, Testac. fluviat. Brasil., 1827, 
p. 26, T. 18, f. 3—6. 
INotes from the Leyden Museum, Vol. XXXVI. 
