78 The Ohio Journal of Science [Vol. XIX, No. 1, 



one would assume a ring canal just outside the bases of the 

 substomial chamber plates and a double radial water tube, 

 one on each side of the ray. Figure 25 and 25A, Plate IV. 



Stages in Development (aboral side). 



The specimens from Lawshe were from 17 mm. down to 

 two-thirds of a mm. in diameter, as stated above. Only a very 

 few of them showed the oral side. 



In the section on the rate of growth attention was called 

 to the great numbers of specimens which were found on single 

 clam valves. The usual size of these abundant specimens is 

 2 mm. in diameter and less. From these specimens showing 

 the aboral face a series has been selected to show the increase 

 in flooring plates. 



The first one, Figure 38, Plate VII, 1.3 mm. in diameter 

 shows the ring of first flooring plates which make the boundary 

 of the substomial chamber. In this specimen the anal pyramid 

 was not to be distinguished and the arms are not numbered. 

 Figures 39, 40 and 42, showing 2, 3, and 4 flooring plates 

 respectively, are drawn to the same magnification as Figure 29 

 and the arms are marked with the numerals they would have 

 if the specimens were oral side up. The anal inter-space is 

 marked with the letter A. 



Only the first and fourth of these diagrams attempt to 

 show all the plates of the aboral side. The specimens are so 

 delicate and the plates so easily disarranged in death and 

 fossilization that it is exceptional in these small-sized specimens 

 to find a pattern that can be worked out completely. 



Specimens 1.3 mm. in diameter from the oral side — Plate 

 VI, Figure 35, shows a group of small animals from the oral 

 side. Several of these are indicated by circles for easier recogni- 

 tion. Figure 55, Plate IX, is a diagram of the plates of a 

 number of specimens. Figure 37, Plate VI is one of the three 

 outlined in Figure 35, but photographed with a higher magnifica- 

 tion. The broad white arrow is pointing toward the anal 

 pyramid, which may consist of four or six plates. The rest of 

 the disc inside the rim is not clear, but is made up of com- 

 paratively few plates. Without doubt this animal has but one 

 row of floor plates and if seen from the aboral side would be 

 like Figure 38, Plate VII. There are just two rows of plates 

 in the peripheral rim. I cannot differentiate radial and inter- 



