2o6 PROCEEDINGS OF THE ACADEMY OF [1879. 



it. In the so-called consolidating plates of Cupressocrinus we 

 find precisely the same structure. Each plate has lateral exten- 

 sions, each of which supports a set of folds which incline in op- 

 posite directions. The number of folds varies in different species, 

 Cupressocrinus abbreviates having apparent! j r seven, and C. gra- 

 cilis but two or three, and so in the Blastoids, Pentremites pyri- 

 formis has seven folds and P. Godoni but five. As the folds of 

 two different plates are not connected laterally, a sort of depres- 

 sion or groove is formed in a radial direction, which evidently 

 contained the food passage, covering the sutures between the 

 plates as the pseudambulacral folds cover those of the deltoid 

 pieces in the Blastoids. The so-called consolidating plates with 

 their folds, of Cupressocrinus, and the deltoid pieces with their 

 appended hydrospires in Blastoids, being not only analogous 

 in position but also almost identical ih structure, it is very evi- 

 dent that they had .a similar office in the animal organism, and 

 that if these organs in Blastoids were respiratory, the hydrospires 

 in Cupressocrinus and Crotalocrinus had the same functions. 



This view r of the relations of the parts under consideration sug- 

 gests a possible analogy in the general structure of Blastoids and 

 Paleocrinoids, in which we may consider that the ambulacrum 

 is a recumbent arm ; the lower part of the forked plate up to the 

 ambulacrum is the first radial in Blastoidocrinus, the oldest 

 known Blastoid,the suture is visible that the two sides of the fork, 

 instead of being interradial, form together a second radial, and 

 the small summit plates are homologous with those which cover 

 the central opening between the oral plates in Cyathocrinus, or to 

 the entire vault in the Actinocrinidas, etc., in which the oral plates 

 do not exist at least not externally. The food groove and ambu- 

 lacral canal are located upon the pseudambulacral fold, which 

 represents the ventral groove in the arms of the Crinoids, and are 

 likewise covered by two rows of alternating plates. If these 

 homologies be correct, it is evident that there is a much closer 

 relation between Paleocrinoids and Blastoids in fundamental 

 structure than has been heretofore supposed, and as we find in the 

 former the representatives both of parallel tubes and folded sacs, 

 it is eyident that their hj'drospires are constructed upon a cysti- 

 dean and blastoidean plan combined. 



We have now noticed the principal forms in which these organs 

 have been observed; there are, however, a large number of forms 



