4 



There can be no donl)l that several more species of regular Echini will be 

 I'ounfl to occur in the Gulf of Siam. The eastern side of the Gulf, to which my 

 researches were confined, is evidently less rich than the western side; and also the 

 median, deeper part of the Gulf doubtless will prove to be inhabited by several 

 species which are not found at the coasts. Upon the whole the Echinid-Fauna of 

 the Gulf will scarcely differ to any extent from the common Indian littoral Fauna. 

 Scarcely any species peculiar to the Gulf will be foimd; the new species described here 

 cannot be maintained to be so. Chcetodiadema granulatum has been taken by the 

 .,Siboga"-Expedition, and I have seen specimens from the sea between New Guinea 

 and Australia and from the Maldive-Islands. PI ear echinus üöderleini also occurs at 

 Samoa, and Pleurech. siamensis has been taken in considerable numbers by the 

 „Siboga"-Expedilion. Gymnechinus pulchellns is as yet only known with certainty 

 from the Gulf of Siam and Singapore. It .seems very jjrobable that all these species 

 will prove to be widely distributed over the Indo-Pacific Region. 



Since the Diadematidœ and Temnopleuridce are so well represented in this 

 collection, I have taken the occasion to study these two families more completely, in 

 the same manner as I have done in my work on the „Ingolf'-Echinoidea I. with 

 the families Cidaridoe, Echinothuridœ, Echinidœ, Toxopneustidœ and Echinometridœ. 

 The present work is then, in some way, a continuation of the „Ingolf"-work. The 

 subjoined attempt at a natural classification of the regular Echini is the result of 

 these very extensive studies. 



By these researches I have made all possible efforts to overcome the 

 numerous difficulties caused by the insufficient original descriptions of most of the 

 species and by the consequently unreliable and very often wrong determinations 

 by later authors. As far as possible I have examined the type specimens. I am 

 very much indebted to the Carlsberg-Fond for having granted nie assistance, en- 

 abling me to visit the large Museums of Europe: the British Museum, the Paris-. 

 Berlin-, Hamburg-, Strassburg-, Genève- and Amsterdam-Museums, where so many 

 types and such rich collections are preserved. Furllur I have in many cases been 

 favoured by receiving in Copenhagen type-specimens of several species for direct 

 comparison with my own material; I am thus obliged lo Prof. Döoeri.ein, Dr. 

 Meissnek, Prof. Douvillé, Prof. Joubin, Dr. Ch. Graviek, Dr. de Meijere, Prof. 

 Bedot, Prof. Théel and Prof. Rosa. — Prof. Bei.i, has kindly sent me to Copenhagen 

 several interesting specimens which I had not time to examine sufficiently during 

 my visit to London, and Dr. Steinhaus has forwarded to me a rich collection of 

 Echinids from the Hamburg Museum for examination. Finally in addition lo 

 several other interesting Echini Prof. S. F. Harmku has [)laced at my disposal the 

 Echinids from the „Skeaf-Expedition, asking me to mention them in my work. 

 All these gentlemen I beg hereby to receive my sincerest thanks. 



By the examination of this large material 1 have found several undesciibed 

 species, mostly wrongly referred to other species. Of these new species I have given 



