Introduction, 



1 he Echinid-Fauna of the Gulf of Siam has not hitherto been especially 

 treated, and only a few species have been stated to occur there. In „Revision of 

 Echini" only the following regular Echini are mentioned from Siam: Teinnopleiirus 

 toreiimaticus, Salmacis rarispina and Heterocentrotiis mamillatiis. In the present work 

 16 species of regular Echini are recorded from the Gulf of Siam, and of these 4 

 are new to science, viz. Chœtodiadema yraniilatiim, Pleiirecliinus Döderleini, PI. 

 siamensis and Gymnecliinus pulchelhis, the first named Ijeing the type of a new genus. Of 

 the 16 species mentioned two have not been taken by the author; one, Temnopleurus 

 Reeoesii was found in the Museum of Copenhagen, labelled Sal min, Gulf of Siam; 

 another, Zic/iino//irj.r calamaris, was taken by the „Skeat'-Expedition on the Malacca- 

 Coast of the Gulf. The species are the following: 



1. Stephanocidaris bispinosa (Lamk). 



2. Diadema saxatile (L.). 



3. Astropyga radiata Gray. 



4. Chœtodiadema granulatum Mrtsn. 



5. Echinothrix calamaris A. Ag. 



6. Temnopleurus toreumaticus (Klein.) 



7. — Reuesii (Gray). 



8. Salmacis bicolor, var. rarispina (Agass.). 



9. — virgulata Agass. 



10. — sphœroides (L.). 



11. — dussumieri Agass. 



12. Pleurechinas Döderleini n. sp. 



13. — siamensis n. sp. 



14. Gymnechinus pulchellus n. sp. 



15. Toxopneustes pileolus (Lamk.). 



16. Parasalenia gratiosa A. Ag. 



]• 



