342 Herbert L. Hawkins — Studies on the Echinoidea. 



Usually in the scales of Elopines the radiating ornament on the 

 exposed area is more conspicuous than in this case; but similarly 

 feeble markings are observable on a scale in the type-specimen of 

 Thrissopater megalops from the English Chalk. 



" The fossil fish-scales from New Zealand thus belong to groups of 

 teleostean fishes which are abundant in Cretaceous formations in 

 other parts of the world." 



EXPLANATION OF PLATE XXI. 



1-36. Aplustrum Selwynensis, sp. nov. Selwyn Eapids. Fig. da x 1J nat. 



size ; Fig. 36 x 5 nat. size. 

 4a, 6. Chrysostoma Selwynensis, sp. nov. Selwyn Eapids. x 3 nat. size. 



5. Trigonia cf. Hanetiana, d'Orb. Waimakariri Gorge. 



6. Holcodiscus (Kossmaticeras) gemmatus, Hupe. Selwyn Eapids. 



7. 86. Belemnites sp. Brighton, south of Dunedin. Maestrichtian (?). 



Fig. 86 x l£ nat. size. 



9. Belemnites sp. Selwyn Eapids. x 1^ nat. size. 



10. Dentalium sp. Selwyn Eapids. x 2 nat. size. 



11. Berycoid fish-scale, outer view, natural size (11a), with portion of 



adjoining covered and exposed areas enlarged four times (116). 



12. Fragments of Berycoid fish-scale, outer view, preserved on inner 



impression of same, three-halves natural size (12a) with portion of 

 exposed area enlarged four times (126). 



13. Elopine fish-scale, outer view, twice natural size. 



[Plates XIX and XX appeared in the July Number.] 



On PI. XX, Figs, la and 6 and 3a and 6 should be transposed, an unfortunate 

 error having occurred in the numbering. The specimen figured at the left-hand 

 top corner really represents Pugnellus Waiparensis, sp. nov., and that at the 

 right-hand top corner represents the normal form of Pugnellus australis, 

 Marshall, from Wangaloa. 



Note. — In some of the copies the following correction is needed at the foot 

 of Plate XIX, which appeared in the July Number Geol. Mag., next p. 304 : 

 forCEET EOUS read CEETACEOUS (two letters AC having accidentally 

 fallen out). — Ed. Geol. Mag. 



II. — Morphological Studies on the Echinoidea Holectypoida and 



their Allies. 



By Herbert L. Hawkins, M.Sc, F.G.S., Lecturer in Geology, University 

 College, Eeading. 



IV. The Perignathic Gtrdle of the Pygasterid^:. 



(WITH FIVE TEXT-FIGUEES.) 



1 . Introduction. 



rnHE examination of the internal structures of Jurassic fossils is 

 _L attended with considerable technical difficulties. Even in 

 cases where the surrounding matrix is sufficiently friable for the 

 development of the external surface, the infilling material is usually 

 either thoroughly indurated or irregularly nodular in texture. 

 Internal moulds may be readily procured, both by natural weathering 

 and artificial processes. But such preparations, though adequate for 

 the investigation of shallow impressions such as the muscle-scars of 

 Pelecypoda, are of uncertain service for the study of structures with 



