492 A. T. MASTERMAN. 
chords which terminate in a pair of well-marked oral grooves, 
or that the pharynx of Rhabdopleura is comparable with 
that of other Diplochorda. Fresh anatomical resemblances 
between Rhabdopleura and Pterobranchia have 
recently been brought out by Harmer! and Ridewood.? 
These need not be recapitulated here, but I believe that when 
their full significance is taken into consideration they will 
necessarily have to be expressed in classification. At present 
I regard the Diplochordaas a natural group comprised of 
at least three natural divisions, namely, Hnteropneusta, 
Pterobranchia, and Rhabdopleura, and possibly the 
Phoronidea. 
The name appears to me to emphasise a fundamental 
character, which now is shown to be characteristic of the 
whole group. 
The monograph of Harmer to which repeated reference 
has been made contains, in addition to a number of new 
observations on the anatomy of Pterobranchia, a discus- 
sion of the inter-relationship of types I have attempted to 
enlign under the title Diplockorda. In his allusions to 
my work on Actinotrocha the impression is given that the 
subsequent workers on similar material have concurred in a 
general disagreement with my results. 
Whilst fully cognisant of certain errors of observation and 
of interpretation in the early work alluded to, I feel that pro- 
egress would be facilitated by pointing out that the subsequent 
authors have differed in their results inter se, quite as much 
as, if not more than, with mine. Until a complete series of 
developmental stages, with ample material, is worked out, 
this state of affairs is likely to continue. 
In the meantime I wish to guard against a false impression 
till the whole subject can be dealt with later in greater detail. 
1 «Siboga Expeditionie,’ Mono. xxvi bis. 
2 «Natl. Autarctic Expedition,’ vol. 11, Pterobranchia. 
