543 TRANS. ST. LOUIS ACAD. SCIENCE. 



condition and nature are not sufficiently known. It consists of 

 little tubes running parallel with each other and roofing in the 

 summit of the calyx in a conical shape (but not the central open- 

 ing). They protrude through the same apertures in which the 

 hydrospires terminate ; there are about five of these tubes to each 

 aperture, which seem to correspond with the plicas of the hydro- 

 spiric sac, and, if they extend down into the interior of the calyx, 

 as I suppose they do, then the only space which could have been 

 occupied by them is below the hydrospiric sac and between the 

 plicas, because they are isolated tubes and consequently not a 

 continuation of the hydrospires. This would explain the neces- 

 sity of the solid support of the plicas, which was undoubtedly to 

 prevent an obstruction in the passage of these tubes, which I take 

 to be the ovarian tubes. 



In regard to the relationship of Echinus and Pentremites, I 

 would say that it seems quite strange to seek for their nearest 

 allies among the Crinoidese ; nevertheless iihey have been regard- 

 ed and classified as a suborder to Crinodeae, even Bronn in his 

 "Klassen und Ordnungen des Thierreichs" puts them below the 

 CrinoidetE, as was done by most ot the authors before, and is still 

 done by others, although Say remarks already, that "in a natural 

 series these bodies constitute the link between the Crinoideae and 

 the Echinidaj."* And Mr. Carpenter certainly cannot point out a 

 Crinoid which bears a stronger resemblance to a Pentremite than 

 a Pentremite does to an Echinus, except those forms which ought 

 to be classified more properly with the Blastoidea, as for instance 

 Stephanocrinus, etc. This is especially true if we divide the 

 test into two halves, as could be done in Pentremites, showing a 

 striking analogy with Echinus. That portion which I had termed 

 "dorsal half" should perhaps have been called, better, " apical" 

 or "ambulacral system"; it would correspond to the ocular plates 

 and ambulacral field in Echinus^ and consists of deltoid pieces 

 and ambulacral field in Pentremites. The ventral portion per- 

 haps also had better be called actinal or interambulacral system, 

 and would correspond to the genital plates and interambulacral 

 field, and consist of basal plates and fork pieces in Pentremites. 

 The growth of these two systems took place always on the apices 

 or uppermost parts of the plates, having the centre or basis of 



* Journal of the Academy of Natural Sciences of Philadelphia, vol. iv., 1825, p. 293. 



