162 PROCEEDINGS COTTESWOLD CLUB 1908 
(ii) There are two species which appear to have emi- 
grated from Dorset, namely, /olectypus hemusphericus 
and Collyrites ovalas. 
Hlolectypus hemisphericus occurs in great numbers in 
Dorset, at about the inter-77we//et-zigzag horizon, and the 
largest specimens are found there. In the Cotteswolds 
specimens are rare, and always small. 
Collyrites ovalis is a common Dorset form, occurring 
apparently in considerable numbers—the individual speci- 
mens frequently attaining large dimensions. It occurs at 
about the same horizon as the last, the inter-77ze//ez- 
zigzag horizon, and has been recorded therefrom in the 
South Cotteswolds; also from the base of the Fullers’ 
Earth (about zzgzag) at Bath and Midford. 
V.—FORMS WHICH ARE PROBABLY THE RESULT OF 
PARALLEL DEVELOPMENT. 
Certain forms occur in both districts, which are 
analogous to one another, and are probably the result 
of parallel development. The following table shows the 
corresponding forms in the two districts. They all occur 
in post-Garantzane beds, and agree only in general 
appearance. 
TABLE V,—APPROXIMATE HOMCGEOMORPHS 
DouttinG-STONESFIELD Forms Doutrinc-Bripport Forms 
eee | = = 
Hemicidaris granulosa, Wright ? Hemicidaris pustulosa, Agassiz 
Stomechinus intermedius (Agassiz) Stomechinus bigranularis (Lamarck) 
Holectypus depressus (Leske) | Holectypus hemisphericus (Agassiz) 
. : Clypeus Agassizi, Wright 
Clypeus Ploti, Klein a4 Si ; g 
| | Clypeus altus, M’Coy 
| 
Stomechinus bigranularis and Flolectypus hemispheri- 
cus are very abundant in Dorset, while the corresponding 
forms in the other districts, namely, Stomechinus tnter- 
medius and [Holectypus depressus, are comparatively rare. 
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