o 



47 



I dare not assert, if it be correct to make a separate family of these forms, though 

 I think it probable. At any rate Duncan is wrong in making Pseudodiadema a 

 synonym of Diadema. As no recent form of Pseudodiadematids is known, it is im- 

 possible to have a full knowledge of their characters. The genus Lissodiadema, to 

 be sure, has only smooth spines, but it can scarcely have any close affinity to the 

 Pseudodiadematidœ, all its characters pointing more towards Echinothrix. 



I must here once more draw attention to the genus Stoinopneustes. I have 

 already (Ingolf-Ech.) shown it to be very different from the Echinometridœ , with 

 which family it was hitherto associated. On the contrary it reminds one in several 

 respects of the Diadematidœ. The spicules are irregular like those of the Diade- 

 matids, though more complicated. The globiferous pedicellariæ recall those of 

 Centrostephanus and its triphyllous pedicellariæ are quite like those of the latter 

 genus. It is very difficult to say, if these similarities are only characters of con- 

 vergence. The difference in the ambulacra (echinoid in Stoinopneustes) and the teeth 

 (keeled in Stomopneustes) is evidently of more importance than the characters fur- 

 nished by spicules and pedicellariæ. It is very unfortunate that no living represen- 

 tatives of forms like Stomechinus are found. It might well be supposed that Stomo- 

 pneustes is a highly specialized descendant of such forms. At any rate the family 

 Stomopneustidœ must be upheld, representing the lowest stage of the Echinoidea 

 with echinoid ambulacra. 



Glyptocidaris crenularis has been referred to the Phymosomatidce ') by Pomel 

 and Duncan; Agassiz, though referring it to the „Triplechinidæ", even thinks it to 

 belong to the genus Phymosoma. I think, Pomel and Duncan are right in placing 

 it in the family Phymosomatidce. The ambulacra are diadematoid (see Rev. ofEch. 

 Pl. VI. 2)"^); the spicules are large fenestrated plates (Rev. of Ech. Pl. XXXVIII. 19). 

 Globiferous pedicellariæ are found, but their structure unfortunately cannot be seen 

 from the figure given by Agassiz (Rev. PI. XXV. 4). 



Having now discussed the relations of the genera of Diadematids, I may give 

 my opinion of the interrelations of the families of the regular Echinoidea. Since 

 I have made a special study of the recent forms of all these families^), except the 

 small and well characterized groups of the Salenidœ and Arbaciidœ, my views on 

 their affinities may not prove unfounded, although they differ considerably from 

 those of previous authors. 



Agassiz (Rev. of Ech.) does not give a more elaborate system, he only 

 names all the families of regular Echinids one after another, all being united into 



') As pointed out by Lambert (Ét. sur quelques Échinides de l'Infra-Lias et du Lias. p. 54) the 

 naine Cyphosoma cannot be used, as it rightly belongs to one of the Coleoptera. 



') In this figure the plate above the adorai one is a small demiplate, the following being the 

 largest. 



') The family Temnopleurldæ is treated below. 



