202 



the genera Spatangus, Echinocardium, Moira, Brissus, Brissopsis, Meoma, 

 and besides a number of other Spatangoid-larvse (Echinopluteus fusus, soli- 

 dus and others) are known to exist. They all of them agree in having the 

 unpaired posterior process, and there is not the slightest reason to expect 

 that there will be any exception to this rule. We have then here a 

 larval type corresponding to the order of the Spatangoidea, 

 forming a distinct larval "order." 



Is it possible to distinguish larval "families" within this order, corres- 

 ponding to the famines of the adult Spatangoids? We are not yet in pos- 

 session of sufficient facts for answering this question definitely; but the 

 facts which are known would seem to point in the direction that also 

 "families" may be distinguished within this larval order. 



The Spatangoid-larvse may be divided into two main groups, viz. 

 those with posterolateral arms and those without. Of the latter group 

 only one species has been referred to its parental form, viz. that of 

 Brissopsis lyrifera; but there is some reason to suggest that also the 

 larvae of the genus Brissus belong to this type (comp. above, sub Brissus 

 Agassizi, p. 119). A larva of the same type, which was found in the 

 Gulf of Panama I would be inclined to refer to Meoma grandis. That 

 would tend to indicate that this larval type is characteristic of the family 

 of the Brissidae. But it can be nothing more than a suggestion at the 

 present state of our knowledge; moreover the fact that Metschnikoff^) 

 has found a larva of this type occurring in great numbers at Triest, where 

 Brissus unicolor, otherwise common in the Mediterranean, apparently 

 does not occur, would seem to prove that this larval type may also be 

 found in other Spatangoids. Metschnikoff refers this larva to Schizaster 

 canaliferus "da sie dort unter den Echinoidenlarven ebenso vorherrschend 

 ist, wie Schizaster unter den erwachsenen Spatangoiden." 



The larvse of the genera Echinocardium, Spatangus and, probably, 

 Moira^) agree in having posterolateral arms, supported by a simple rod, 

 not widened at the base. This would point in the direction of this larval 

 type being characteristic of one group of Spatangoids. The existence of 

 several species of the type of Echinopluteus fusus might indicate that this 



1) E. Metschnikoff. "Studien uber die Entwickelung d. Echinodermen u. Nemertinen." 

 Mem. Acad. St. P6tersbourg. VII. S6r. XIV. 1869. p. 46. Taf. VIII— IX. 



2) Caswell Grave has reared the larva of Moira atropos through metamorphosis, but 

 unfortunately does not give any information of the shape of the larva. On my applying 

 to him for the information wanted, he kindly sent me some sUdes containing some of the 

 larvse. It turned out, however, that there were two different species of larvse in the slides 

 one with posterolateral arms, the other without. Having called liis attention to this fact 

 I was informed by him that he thought it almost certain that the form with the postero- 

 lateral arms was the Mo/ra-larva, but full certainty could not be obtained any more from 

 the material still preserved. 



