56 FIRST RECORDED OCCURRENCE OF BLASTOIDEA IN N.S. WALES, 



Two slight ridges running across the radial in specimen A (see 

 tig. 1 ) might be thought to represent a deltoid and basal suture 

 respectively. But the former, about 1*5 cm. from oral end, is 

 not matched on the other limb of the same radial, while the 

 ridge across the lower portion of the radial (1*5 cm. from aboral 

 end) of similar appearance would make the portion cut off too 

 short for a basal. The interradial suture runs straight along 

 the edge and would probably not be prolonged to form an inter- 

 basal suture as the former supposition would require. It may 

 be mentioned that in specimen B [in external cast] a somewhat 

 similar crack appears in the lower portion of the radial, but in 

 this latter case the concentric ornamental striae of the radial 

 obviously cut right across the pseudo-suture in a manner 

 suggesting that the latter is quite accidental. 



Ambulacra. — These areas are relatively narrow, and, as stated, 

 decrease from - 3cm. very gradually to the aboral sinus. Fig-3 

 is a sketch of portion of the ambulacra of specimen A. It 

 shows the transverse ridges (between which were the side plates) 

 and the food groove down the centre. Sixteen of these ridges 

 (g) are preserved, indicating about 40 over the whole length of 

 the lancet plate. These plates seemed to have covered over the 

 lancet plate, which arrangement would be in accord with the 

 characteristics of the Troostoblastidse. 



Lying outside the side plates, and at a higher elevation, the 

 outer side plates conform roughly with the former. The ridges (s) 

 between these outer plates lie over the canal (c) shown in tigs. 3-4. 

 This canal probably represents that which runs above the 

 hydrospires. The three subsidiary ridges between each pair of 

 larger ridges (s) probably are only ornamental, and may represent 

 three grooves on the lower surface of each outer side plate. They 

 are shown on the right of fig. 3. 



Transverse sections of A and B were made but did not show 

 what the structure of the hydrospires was like. Two canals (c) 

 mentioned above were cut through, but the internal structure 

 of the blastoid is not preserved in the specimens obtained. 



The surface obtained from specimen B by taking an impression 

 in wax is indicated by the broken line in fig. 4. A long lancet- 



