74 
A Study in Variation. 
but are more evenly spread out, indicating the possibility of 
a stout specimen even at an early age. The arithmetic mean 
of the deviations is 6.642 or 12.26 per cent, of the mean, so 
that the general conclusion is that the specimens of Pugnax 
pugnus Martin have a tendency to rotundity in all phases of 
growth. 
Variation in Pugnax cf. sulcatus (J. de C. Sow) — The 
second form which is contained within the lesser peaks does 
30 60 7° 80 
Fig. 4b. 
not fall readily into any species, but the nearest named 
species is Pugnax sulcatus (J. de C. Sow). Parkinson (4) in 
describing this species says : ‘ Pugnax sulcatus, as here 
interpreted, even excluding the varieties described below, 
varies within somewhat wide limits. Occasional specimens 
are almost identical with the type (5) but the majority are 
smaller and rather more flattened.’ The species here con- 
sidered is very like the one figured by Parkinson (6) as a 
transitional form between sulcatus and the forms with a 
rounded sinus. 
In this species there is no need to examine the relation 
height_ x I00 s i nce it would give the same results as in the 
breadth ° 
case of Pugnax pugnus (Martin). 
The relation x 100 shews the mean relation to 
The Naturalist 
