HOMCEOSOLEN. 
87 
Talue of S. gamhlei is that d’Orbigny regarded the two as only 
indiridual variations of one species ; he represented the pinnate 
zoaria as only the older stage of the other. Age is, however, 
certainly not the explanation of the differences between the two 
series, for the pinnate character is well developed in specimens 
that are much smaller than some typical forms of H. ramulosus. 
"Weightier evidence agaiust the establishment of H. gamllei is 
that some specimens of that form (e.g. one of B. 3740) show 
a tendency to a flamboyant, dichotomous branching, and that 
often of two specimens from the same locality (e.g. B. 102 from 
Charing) one may belong to each species. In this case, however, 
as the material collected by" Harris at Charing was obtained from 
the gullies in the Chalk escarpment after rain, the specimens may 
have come from different horizons. 
A^evertheless, the difference between the well-developed forms of 
the two species is so marked that their separation is advisable, though 
H. gamhlei may be only a variety of H. ramulosus with a pinnati- 
form zoarium. The argument which has decided me in favour of 
separating I£. ramulosus and U. gamhlei as distinct species is that 
the division into two types, that with hooked, irregular branches 
and that with a pinnate zoarium, is marked in specimens of all 
stages of growth. The contrast is shown in the thin terminal 
branches in D. 677 {gamhlei) and D. 678 {ramulosus), and in the 
young basal specimens — the Supercytis digitata form — by D. 668, 
of which the best-preserved branch has the pinnate plan of 
gamhlei, while D. 4506 (a young form with very thin branches) 
and D. 404 (with thicker and more crowded branches) have the 
characters of H, ramulosus. 
The species is named after Hr. Gamble, who has collected a fine 
series of both it and ramulosus, and recognized that a part of the 
series belongs to a distinct variety. 
LIST OF SPECIWEHS. 
D. 2948. A large, nmch branched zoarium ; the front is 65 mm. wide, and some 
branches are 50 mm. long. Figd. by Lonsdale as R. ramulosus. 
Dixon’s Geol. Sussex, pi. xviiiB, fig. 4 {non figs. ‘^b-d). Lpper 
Chalk. Bromley, Kent. Bowerbank CoU. The reverse is weU 
carinate ; in 17 mm. length of a branch are five branchlets on one 
side and six on the other. 
D. 2949. The type-specimen. A small part of the base has been figured by 
Lonsdale in Dixon’s Geol. Sussex, pi. xviii n, fig. 5*. The frond 
