20 Trans. Acad. Sci. of St. Louis. 



manner of folding. They are in an end view not unlike an un- 



symmetrical figure 8, — see Fig. 11, 

 — of which the upper loop is larger 

 than the lower one. These loops, 

 in large specimens of Pentremites 

 sulcalus, are one fourth of an 

 inch long. Counting five folds to 

 each of the ten cylinders, or ten 

 to each ambulacrum, it would give 

 for the whole body, if stretched out, a ribbon over two feet 

 long — an organ well adapted for respiratory function as sup- 

 posed by Billings.* The apices of these foldings are often 

 found to have coalesced with the calcareous base part of the 

 fork pieces as observed in Pentremites conoideus and others, 

 whereas the plicae of the other end rest in those plications or 

 grooves of the deltoid expansion already described near the 

 summit openings. The coalescing with the calcareous base 

 portion of the fork pieces is not a peculiarity found only in 

 certain species as indicated by Carpenter, f but it can be 

 observed in other species, as in Pentremites Jlorealis, etc. 

 Between the upper loops of these plications, which are kept 

 open by resting in the little grooves near the summit, we find 

 longitudinal tubes, protruding through the genital openings 

 on the summit and filling them completel}^ These tubes I 

 regard as the ovarian or genital tubes. They are found (in 

 well preserved specimens) to be filled with little round bodies 

 (eggs?). Fig. 6, Plate II., is a longitudinal section through 

 the upper loop of a hydrospiric cylinder of Pentremites 

 jlorealis, exhibiting these little round bodies at various places. 

 The supposition that these are ovarian tubes is strengthened 

 by the fact that the plications near the summit rest in 

 grooves, which would be necessary to prevent any obstruction 

 to the passage of the &^g. 



In Cadaster the construction of the hydrospires is quite 

 different. Here we have from the roof of the calyx vertical 

 lamellae one eighth to one fourth of an inch long, reaching 



* Billings, Loc. cit., p. 103. 

 t Carpenter, Loc. cit. 



