Chætodiadema granulatum n. g., n. sp., 
a new Diadematid from the Gulf of S i am. 
By 
Th» Mortensen, Dr. ph.il. 
Among the Echinids which I collected in the Gulf of Siam in 
1900 a most interesting new form of Diadematids is found, allied to 
Astropyga, but differing from that genus and all other Diadematids 
especially by its peculiar pore areas. — Though I am no friend of 
preliminary reports, I think it right in this case to give a prelimi- 
nary description of the form concerned, as it will probably take a 
rather long time, before the final report can be published. The 
full description with figures will appear in: The Danish Expedition 
to Siam 1899—1900. Results of the Zoological Collections made 
by Dr. Th. Mortensen. (Kgl. Danske Yidensk. Selsk. Skrifter, naturv. 
og mathem. Afd.) 
The test is greatly depressed and very flexible. The abactinal 
side looks much like Astropyga. The apical area is large, but 
the genital plates are not much elongated; inside the genital and 
ocular plates tliere is a rather broad band of small, irregular plates, 
carrying small spines. A small genital papilla is found, covering 
the genital openings. The interambulacral areas do not on the abac¬ 
tinal side differ in any essential character from those in Astropyga. 
In the outer series of large tubercles the uppermost one is found 
on the 9—10 th plate from above, and there is no distinet series 
of secondary tubercles on either side of this series, only irregularly 
placed miliary tubercles. The inner series of interambulacral 
1 
Vidensk. Meddel, fra den naturh. Foren. 1903. 
