TRANSACTIONS OF SECTION C. 513 
Parabolinelia triarthrus, Call., sp. 
Leptoplastides Sailteri, Call., sp. 
Megalaspis Homphrayt, Salter, sp. 
Orometopus elatifrons, Ang., sp. 
Triarthrus shinetonensis, sp. nov. 
Dicellocephalina furca, Salter, var. 
Symphysurus Croftii, Call., sp. Symphysurus microphthalmus, sp. nov. 
Agnostus dux, Call. Desmus Cobboldi, gen. and sp. nov. 
Euloma monitle, Call., sp. Agnostus Callaret, Raw. 
Shumardia pusilla, Sars., sp. Pierocephalus hemicycloura, gen. and sp. 
Lichapyge cuspidata, Call. nov. 
All except the last have been obtained from the main fossiliferous horizon in 
Shineton brook, and a comparison with the latest and most complete list of the 
fauna of the Ceratopyge series of Scandinavia, given by Moberg 1906, indicates 
that this horizon falls within the Shuwmardia zone of that author, while the com- 
plete fauna of the shales indicate that they include also the Bryograptus and 
Dictyomena zones below. 
5. The Development of Olenus Salteri, Call. By F. Raw, B.Sc., F.G.S. 
Among the specimens from Shineton collected by Mr. Rhodes for H.M. 
Geological Survey are some small slabs covered with minute individuals of Olenus 
Saltert, Call., so that the early stages of growth are well represented, and it has 
been possible to trace the development of this species from individuals with only 
two thoracic segments upwards. 
The adult reaches a length apparently of 14 or 23 inches, but only two 
specimens indicate such sizes. The head closely resembles that of Leptoplastus, 
e.g., L. stenotus, Ang., the free cheeks bearing exactly similar spines. The eyes, 
however, are somewhat closer. The thorax, too, is very similar, having exactly 
the same shape of pleural ends, though the axis is much broader in proportion. 
The tail, however, is quite different from that genus, being broader than long, 
emarginate behind, and entire, as against triangular and toothed. 
But as the form is traced back from the adult through younger and younger 
individuals considerable changes appear. The tail becomes toothed and pointed, and 
finally very spinose. The ends of the thoracic pleure become long backwardly 
directed spines. The glabella, sensibly smooth in the adult, becomes segmented and 
narrow, and furnished with prominent eye-lines, The cheek-spines take a more 
forward position, and two additional pairs of spines appear. 
With a few less segments than the adult there is a definite Leptoplastus stage, 
_ while an earlier stage still, with seven segments, is very close to such an early 
Parabolina, as P. acanthura. These later stages of development can, the writer 
thinks, be taken as indicating the evolution of the form, and so as pointing out 
its systematic position. As to the latter we cannot refer it to any existing sub- 
genus of Olenus. Superficially it approaches nearest to Cyclognathus costatus, 
Brogger, from which the head differs in bearing spines, and in having a frontal 
limb, characters which again connect it with Leptoplastus. Indeed it can hardly 
have been derived from any other known genus. From comparisons of adult 
Oleni, and their succession, and from the development of O. Salter, there appears 
to the writer to have been in several branches of the Olenus family a similar or 
parallel evolution, the tail changing from spined triangular to entire rounded, the 
spines being also often lost on cheeks and axis, the ends of the pleure changing 
from long-spined to rounded, and the glabella often becoming smooth. Examples 
of this in whole or in part are seen, the writer thinks, in the derivation of Cyclo- 
gnathus from Peltwra, and further back perhaps from Leptoplastus, Acerocare 
perhaps from Leptoplastus, Parabolinella from Parabolina, Misses Crossfield and 
Skeat’s Peltura punctata from the Shineton Triarthrus. (See last abstract.) 
For Olenus Saltert the writer would therefore propose the sub-genus Lepto- 
plastides, and would include in the same sub-genus the <Acerocare claudicans, 
A. norvegicum, and A. paradoxvum of Moberg. 
1907. Li 
