804 PEOF. A. DENDY AND MR. R. W. H. ROW ON 



cannot be very ancient, because hardly any of their fossil remains 

 have been discovered, but this may possibly be accounted for by 

 the fact that they do not possess a coherent skeleton, and 

 accordingly become disintegrated soon after death. 



It is, however, quite possible that some of the veiy imperfectly 

 known extinct Pharetrones may really be offshoots from this 

 family, as we believe to be the case with the recent Lelapiidte. 

 The customary association of the latter with the Pharetrones 

 is based upon the presence of a fibrous skeleton composed of 

 modified radiates, especially the tuning-fork spicule, and a 

 fibrous skeleton of this type is perhaps present in some of the 

 extinct genera. We have, however, purposely avoided discussing 

 the latter in this paper, as we do not know enough about them 

 to warrant us in drawing any but the most general conclusions. 

 As we have already jDointed out, the apical position of the nucleus 

 of the collared cells in Lelcqna, and the presence in it also of 

 subgastral sagittal tiiradiates, render the Grantiid origin of the 

 Lelapiidte reasonably certain. 



In addition to the Lelapiid?e, one other family, the Amphoriscidse, 

 seems to have originated from the Grantiid stock. This family 

 derives its distinctive character fi'om the development of strong, 

 centripetally directed apical rays on the tangential radiates of 

 the dermal cortex. Such apical rays have undoubtedly appeared 

 several times independently in the evolution of the Calcarea. 

 "We find them, for example, in some species of Leucetta, in 

 Leiocaltis, in some species of Leucettusa, in one species of 

 Grantia {G. intermedia), in some species of Leucandra, and in 

 Grantilla, as well as in this group. It may well seem doubtful 

 whether, in view of these facts, the character in question ought 

 to be regarded as of family significance in the Amphoriscidse ; 

 but inasmuch as the latter appear to us to comprise a natural 

 assemblage of three closely related genera in which this character 

 is no longer casual but has assumed great importance in the 

 structure of the skeleton, we have decided to retain the group, 

 at any rate for the present. We have, however, considerably 

 reduced the size of the family by the removal of Leucaltis 

 (Heteropegma), together with some of the species formerly 

 placed in Leucilla, but now divided between Leucetta, Leitcettiosa 

 and Leucandra, to which they seem to be more closely afliliated 

 by other characters, leaving in the genus LetociUa a group of 

 species which are, we believe, all directly descended from 

 Ampkoriscus. 



The most primitive Amphoiiscidse, belonging to the genus 

 AmphorisGUS, have a syconoid canal system and a somewhat 

 feebly devel(^ped dermal cortex, and we accordingly consider the 

 family to be an offshoot from low down on the Grantiid stem. 

 Finally, we may point out that in this family again the canal 

 system has undergone its usual transformation from the syconoid 

 to the leuconoid type, with intermediate sylleibid forms. 



