44 ECHINOIDEA. II. 



specimens the fasciole is generally distiiict, whereas in larger specimens it gradnally becomes less 

 distinct on acconnt of nnmerons .small niiliary spines, like those of the fasciole, developing betvveen 

 the primary spines on the adjacent part of the plastron. Loven is scarcely right in maintaining that 

 the e.xtension of piates I. a. 4 and V. b. 4 can in no wise be compared with the extension of piates I. a 

 6 ^ X and V. b. 6. -(- >^- in Prymnodesinic Spatangidæ. It is a faet of importance for this qnestion that 

 in Bn'xsops/s ( Toxohrissits) pacifica and the species cloigata described below the first extended plate 

 is not the 6th bnt the /th — a case nnknown to Loven'; had he known this, he wonld probably not 

 liave laid so mncli stress on the numero 6. I think it not iinreasonable to conclude that, when the 

 subanal fasciole of the Prymnodesmic Spatangidæ includes sometimes the jjlates L a. 7 -j- x and V. b. 7 

 -)- X instead of 6 -[- x (and nobody will donbt the horaology of the fasciole and extension of piates in 

 this case), it mav also be possible to regard a fasciole inclnding only the extension of piates L a. 4 and 

 V. b. 4 as homologons with that of the Prymnodesmic Spatangidæ- — and that likewise will hold 

 good for the extension of this plate, in case the fasciole is wanting, whether it has disappeared with 

 age or was never formed. That only one plate extends so as to reach within the fasciole cannot be 

 against the homology. In the yonng Ec kino c ar din 111 cordatuvi likewise only one plate extends within 

 the fasciole, viz. the 6th, as is described below. The faet that only one plate extends within the fasciole 

 in U. iiarrsiaiius thns evidently marks tiie fasciole of this species as being very primitive and of 

 an embryonal character. — Otherwise, if it be right what Lambert (Etudes sur le plastron des 

 Spatangides) and de Meijere ( Siboga-Ech. p. 153) maintain that the Amphisterni have not devel- 

 oped from the Meridosterni, (and I, for niy part, am fnlly convinced that the\- are right lierein), the 

 fasciole evidenth' will ha\-e developed independently in each group, and it is thns not surprising to 

 find some differences in its relations in the two groups. Be that as it will, it is certain that the forms 

 without a subanal fasciole agree exactly with those provided with a fasciole in the structnre of the 

 ambnlacra of the bivium; there cannot be distinguished two groups, one without, the other with a 

 subanal fasciole, as was suggested by Dun c an. 



Nevertheless Duncan was certainly right in suggesting that Agassiz has confounded two 

 species under his Urechhius naresianus in the Challenger -Report. On an exammation of the speci- 

 mens of Ureck. naresianus in the British Museum I find that those from »St. 158 are not really that 

 species; their globiferous pedicellariæ differ so considerably from those of naresianus. that they can 

 certainly not belong to this species; they agree exactly with those of Cystech. Wywillii (comp. below 

 p. 49). Probably these specimens will prove to belong to this latter species; since, however, Cyst. Lovcni 

 and Urcch. gigantrus also have similar globiferous pedicellariæ, I shall not tr>- to decide to which 

 species these specimens really belong, but be satisfied with having shown that they are not )iarrsiaiius. 



As pointed out by Loven it is the 4th ambulacral plate in the .series La and V. b which ex- 

 pands internally to meet the episternal angle, and this is a very constant feature. Among the nume- 

 rous specimens I have examined, I have found only two exceptions: in one case the plate I. a. i is 

 abnormally divided into two piates with one tentacle each, the plate with the episternal prolongation 



! .Vlso in Micraster coranguinuni tliere is some irregularity in this respect, it beiug the \'. Ix 5 which reaches the 

 fasciole according to the analysis of the test given in Lovén's: Etudes. PI. XXXIII. 



^ In Urechhius gigan/eus it is the 6th plate which is extended (Pananiic Deep-Sea Echini. p. 154. Fig. 221 1 ; no fasciole, 

 however, has been observed in this species. 



