85 
the upper extremity of the middle branch is not much below that 
of the upper branch. This is a variation known to occur in other 
species, and I can detect no other difference. 
D. tydemanni was originally described from the Malay Archipelago. 
Possibly it is only an aberrant form of D. nierstraszi from the 
same seas. 
Dichelaspis cor, C. W. Aurivillius. 
An nand ale, Mem. Ind. Museum, vol. ii, p. 119, pi. vi, figs. 7—10. 
There are two lots of specimens in the collection, one on the 
gilis of Scylla serrata (“Gulf of Siam”), taken 23—ii—1900, the 
othei, without data as regards the host, taken on the next day 
near Koh si Chang. 
All these specimens, the valves of which exhibit very much 
the same variation as commonly occurs in the species, are distin- 
guished from the typical form by the possession of a small dark 
spot on each side of the capitulum at the inner margin of the 
upper branch of the scutum near its upper extremity. I think 
they may therefore be regarded as the type specimens of a new 
variety, which may be named D. cor var. bipunctata. I call this 
form a variety and not a subspecies or local race (see Mem. Ind. 
Mus., vol. ii, p. 67), because there is no evidence forthcoming at 
present that it is peculiar to the Gulf of Siam. As regards anatomy 
the new variety agrees closely with the typical form. 
D. cor is widely distributed in the warmer parts of the 
Indian Ocean. 
Fam. Iblidæ. 
Ibla cumingi, Darwin. 
1. Cumingi and I.sibogæ, Hoek, Cirr. Siboga Exp. (Monogr. xxxi a), pp. 
47, 48, pi. iv, figs. 20—22, pi. v, figs. 1—8. 
Among a number of typical specimens of Ibla cumingi taken 
by Dr. Mortensen at Koh Lom (W. of Koh Chang) on 3— 
iii—1900 I find four individuals wbich must be referred to the 
