189 



individual plates, but this was impossible in many cases, which may 

 indicate one of two conditions: 1) that the specimen was very old 

 and the plates had fused as is characteristic of this form in old age; 

 or 2) that for some reason the plates in certain regions had become 

 more firmly united. I believe that the second alternative is correct, 

 because two regions diametrically opposite alone remain as an almost 

 solid plate, whereas in an "old" specimen the fusion of plates is more 

 uniform. 



The aboral surface shows an almost bilateral symmetry, with a 

 line drawn through the anus and the anal inter-radius, the anus in 

 this species being situated on the edge of the flattened test (Fig. 1, 

 an.). The apical system, normally central in position, is excentrically 

 placed, having moved away from the anus towards the opposite side, 



Fig. 1. 



a/mèU 



Fig. 2. 



la.f: 



Fig. 1. Echinarachnius parma, aboral view, showing plates, ambulacra and 

 inter-ambulacra, an, anus; amb. I — amb. V, ambulacra I— V; i. a. 1 — 5, inter-ambu- 

 lacra 1 — 5. 



Fig. 2. Echinarachnius parma , oral view, showing arrangement of plates. 

 avy anus. 



but in a straight line (Fig. 1). This migration greatly elongates certain 

 ambulacral and inter-ambulacral systems, and shortens or twists others. 

 Thus, in Fig. 1, ambulacra II and III and inter-ambulacrum 3 are 

 much longer than normal, i. e., than when the apical system is central; 

 while ambulacra I and IV have become so twisted that they mainly 

 lie opposite, or 180° apart, instead of 75°, as is the normal position. 

 Ambulacral system V is almost lacking, a few pores being all that 

 remain, and there are through plates that are more like the plates of 

 an inter-ambulacrum (Figs. I and 3, Amb. V). Thvis the plates and 

 pores of ambulacra I to IV are normal in number and relations, being 

 changed only in size and shape to accommodate the changed location 



