Nov., 1918] Structure of A gelacrinites and Streptaster 71 



the length of the plate at right angles to the W into which 

 the tops of the W like ridges merge. From this ridge posteriorly 

 the plate extends toward the anal pyramid about the same 

 distance as from the proximal part to the ridge, becoming thinner 

 all the way until it unites with the other plate of the posterior 

 inter-radius. 



The same plate shaped somewhat differently and not 

 differentiated at its left (aboral) end from the rest of the plates 

 is shown in the aboral diagram of Streptaster, Figure 48, Plate 

 VIII. 



Foerste states that the two anterior peristomial plates are 

 represented on the aboral side by triangular ridged plates in the 

 Miller and Faber specimen. Figure 6, Plate I, represents a 

 side view of an ^ . pileiis which has lost its arms 1 and 5 and the 

 posterior plate P. This same specimen is photographed from 

 the oral side in Figure 4, Plate I. The R. and L. peristomial 

 plates are shown edge on and as far as this specimen is concerned 

 the plates appear thickest at the peristomial face and seem 

 to thin out in the anterior direction. 



In the best preserved of the Lawshe specimens the sub- 

 stomial chamber is bounded definitely by the five first flooring 

 plates with their projecting lateral processes and the posterior 

 peristomial plate. See Figure 44, Plate VII. In other individ- 

 uals this is not so plain. In one instance it appears as if a 

 lateral process of a first flooring plate is cut off short and is 

 connected with the lateral process of the flooring plate of the 

 next ray by a small plate of its own width abutting directly on it. 



The condition of the peristomial ring which corresponds 

 with the Miller and Faber A. pileus is shown in the aboral 

 diagram of Streptaster, Figure 48, Plate VIII. Here we have 

 the first floor plates of rays 1 and 2 united closely, a plate pro- 

 jecting aborally between the first flooring plates of ray 2 and 

 ray 3, a somewhat similar plate projecting between the first 

 flooring plates of ray 3 and ray 4 and the first flooring plates 

 of rays 4 and 5 closely united. 



If we consider the oral surface again it is clear that this 

 condition might have been, expected. The oral slit is elongate 

 from right to left, the rays 1 and 2 closely approximated at 

 their proximal ends, the rays 4 and 5 also closely united and 

 both sets distinctly separated from the anterior ray. In 

 A. austini, at least in the variety lawshe and in the small 



