406 PROCEEDINGS OF THE. MALACOLOGICAL SOCIETY. 
Dimensions.—Largest example, 20 by 20 mm.; smallest example, 
15 by 15mm. 
This ornamental shell belongs to Agassiz’s group Clavellate. Its 
delicate and regular sculpture suggests affinities with 7. formosa, 
J. de C. Sowerby, 7. Phillips?, Morris & Lycett, and 7. Moutieriensis,' 
Lycett, species which occur in the Lower Oolitic rocks of England and 
the Continent. In the general character of its costal system it comes 
perhaps closest to 7. Phillipsi, although in that form the shell is more 
convex, more tubercled in its ornamentation, and the costs descend 
more abruptly (almost perpendicularly) from the marginal carina, 
which is nearly straight or not so excavated as in the Borneo shell. 
In figure it is very similar to 7. Moutdtertensis from the French Oolites, 
but that again exhibits differences, having fewer cost, wider inter- 
costal sulcations, and a coarser sculpture. 
Further differences also separate the Borneo shell from 7. formosa, 
which has a much wider area and smooth sulcations between the 
coste, instead of the club-shaped structures peculiar to the present 
species. The oblique striations on the clavate ridges within the costze 
do not appear to have been noticed before in connection with the shell- 
structure of Zrigonia, although minute lineations can be seen on an 
allied Lower Oolite form known as 7. striata of James Sowerby, 
occurring between the cost and on the obtuse tubercles which 
ornament their summits. It is one of the few species of Clavellate 
Trigonias which show a regular and symmetrical ornamentation. 
More often the sculpture of this group exhibits large tubercles 
irregularly placed over the surface; such forms are generally typical 
of Middle and Upper Oolite horizons, whilst the more regularly 
ornamented species appear to characterise deposits of Lower Oolitic age. 
Both the ferruginous rock and the ‘cindery’ material contain this 
species. Two specimens occur in the former, showing internal and 
external characters; the crenulations on the diverging teeth, however, 
being very obscurely seen. They are furnished with about 15 rows 
of cost, but mineralization has somewhat spoilt their original natur: . 
characters, so that the finer structures are not very apparent. The 
actual sculpture is best depicted in the specimens found in the grey- 
cindery rock, that occur only as hollow casts; but by means of wax 
impressions all the external details of structure have been reproduced 
with excellent results. 
One of these specimens exhibits a well-marked, beautifully striated 
tooth, lying beneath the escutcheon area; it forms part of the 
example represented in pl. xv, fig. 2. A rough east of a Zrigonia of 
larger size than the foregoing occurs in the pyritized siliceous rock, 
but it is not sufficiently well preserved to allow of identification. 
2. Prorocarpra crassicostata, F. Vogel. 
Protocardia crassicostata, Vogel : Samml. geol. R.-Mus. Leiden, 
vol. v (1896), p. 140, pl. ix, figs. 1-5. 
1 Further information respecting these species will be found in John Lycett’s 
‘* Monograph of the British Fossil Trigoniz ’’ (Pal. Soc. Monog.), 1872. 
