164 
Dr. A. Gunther on the Occurrence of 
Fam. 15. Reteporidse. 
Smitt has also discarded this family in his latest paper* *, 
and distributed its members. In this I do not see my way to 
agree with him at present. The structure of the zoarium in 
Retepora is so remarkable and significant that it seems to 
me to be rightly regarded as the basis of a family. It seems 
hardly probable that forms exhibiting this marked zoarial 
peculiarity would be developed sporadically in various groups. 
It is a more reasonable supposition that the species in which 
it exists are closely connected genetically. 
In taking this view I assume that the structural differences 
between the zoarium of Retepora and that of the other allied 
Cheilostomata go much beyond the mere reticulate character 
of the branchingf. 
Our two British species of this family may be ranked under 
one genus. 
Genus Retepora, Lamarck. 
Species: R. Beaniana , King. 
R. Couchii , Hincks. 
The foregoing is little more than a mere indication of results. 
The detailed observations on which they rest and the discus¬ 
sion of doubtful points must be reserved for my ‘ History.’ 
No one who has not attempted to frame a natural classifica¬ 
tion of the Polyzoa can appreciate the peculiar and perplexing 
difficulties attendant upon the work. Those who have done 
so will best understand how much indefiniteness must of 
necessity attach to any system we may devise, how flexible 
and accommodating it must be to fit in with the facts of 
nature. 
XVIII. — On the Occurrence of a Land-Rail (Rallus) in the 
Island of Aldabra. By Dr. A. Gunther, F.R.S. 
In the year 1876 Commander Wharton started in H.M.S. 
‘Fawn’ on a voyage of survey to the East-African coast; and 
* “ Recensio systematica Bryoz. quae ad insulas Novaja Semlja et ad 
ostium flumiuis Jenisei inven^runt Doetores A. Stuxberg et II. Theel,” 
CEfv. Kongl. Vetenskaps-Ak. Forhandl. 1878. 
t A difficulty occurs in the case of the Membranipora siyillata, Smitt, 
described in his ‘ Floridan Bryozoaf which, according to his account, 
combines a true Membraniporidan cell with a Reteporine mode of growth. 
But, on the whole, at present, the reasons for preserving the family 
seem to me stronger than those for dismembering it. The point requires 
more extended investigation. 
