130 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
does good service in redescribing the structure of both these Silurian 
genera. As to the first, he concludes that it is an Echinid and not a 
Cystid ; and as to the second, that it also is an Echinid and not an Asterid. 
The diagnoses of the Cystoidea lately offered by Prof. v. Zittel and 
Prof. Haeckel are considered, and it is strongly urged that they do not 
enable us to draw any sharp line of distinction between the Cystoidea 
and the Echinoidea. 
The masticatory apparatus of the two genera is described and 
discussed, and it is shown how they may be found to explain the origin 
of the same apparatus in gnathostomatous Echinoids. Dr. Gregory joins 
in the attack on the Lovenian doctrine of the homologies of the 
“ calycinal plates,” and suggests that the plates so called in Echinoids 
are homologous with the plates of the valvular pyramid of the Cystoidea. 
Affinities of Echinothuriidae.* — Dr. J. W. Gregory comes to the 
conclusion that the apparently primitive features of these Echinoids are 
secondarily acquired and are not primeval. The recent genera, therefore,, 
are extremely specialised and not primitive forms. The family should 
be regarded as belonging to the order Diademoida, and as derived from 
the Pedinidse. The oldest member of the family appears to be Pelane- 
chinus, and the flexibility of the tests of the existing Asthenosoma and 
Phoronosoma is regarded as due to a diminished calcification of the 
plates. 
The author describes a new genus Pcdinothuria, and gives reasons for 
regarding it as a connecting link between the Pedinid® and the Echino- 
thuriidse ; another new genus — Helikodiadema — has a flexible test, duo 
apparently to its deep-sea life ; it is a modified form of Pseudodiadema. 
Holothuriidse of Norway.! — Mr. Hj. Ostergren reports that Stichopus 
griegi sp. n., S. tremulus, and H. ecalearea are the only Norwegian 
Holothurians that belong to the true Holothuriidee. The new species is 
said to be closely allied to S. tremulus , but, though he has only a single 
specimen on which to found his judgment, the author appears to have 
satisfied himself that it is specifically distinct. 
Synallactinae.! — Herr Hj. Ostergren has made a study of some forms 
thought to be well known, and finds that their anatomy has not been 
thoroughly investigated. For example, the long known Holothuria 
intestinalis is shown to be a Mesothuria , of which a fresh diagnosis 
is given. Similarly Sars’ Stichopus natans is found to belong to the sub- 
family lately instituted by Professor Ludwig, and it is necessary to 
make for it a new genus which the author calls Bathyplotes ; Stichopus 
tizardi of Theel must be put into the same genus, and apparently others 
also. 
With regard to the systematic position of the Synallactinee the author 
does not agree with Prof. Ludwig : the latter, it will be remembered, 
regarded them as a sub-family of the Holothuriidge, and as forming 
a link with the Elpidiidae. Herr Ostergren thinks that their points 
of resemblance to the Elpidiidas are so great that they ought to be 
placed in that order ; the two families just named may, with the Pelago- 
* Quart. Journ. Geol. Soc., liii. (1897) pp. 112-22 (3 figs.), 
f Bergens Mus. Aarbog, 1896, No. 12, 10 pp. and 1 pi. 
j- Festskrift for Lilljeborg, Upsala, 1896, pp. 347-60 (1 pi.). 
