Hyatt.] 
346 
[Dec. 2. 
sometimes truncated, and have only faint longitudinal ridges 
without scales. 
O. papyracea sp. Stoppani occurs in the Trias. 
. C. cuneata Quenst. (not Morris & Lycett), similis Chap, et 
Dewal., j&ssa sp. Goldf., semistriata Terq., are in the Jura. 
Pinna minuta Gabb, of the Cretaceous, may belong in this 
group but I have failed in finding any species in the Tertiary. 
The only species in the existing fauna seem to be C. incurvata 
sp. Chemn., and rumpliii sp. Hanley. Reeve accepted the latter 
as a distinct form although it seems to be very closely allied to 
C. incurvata. 
The shells of the second subdivision have longitudinal ridges, 
and scales although not usual are sometimes present . 1 The ven- 
tral area often grows equal in length to the dorsal and the valves 
are broad at the posterior end giving a truncated aspect. In many 
species, however, the posterior ends of the valves have the same 
outline as in the first subdivision. 
C. lanceolata sp. Sow. and Goldf. is found in the Jura . 2 
C. sublanceolata Eichwald, robinaldina and renauxiana sp. 
D’Orb., petrina sp. White, and laqueata sp. Conrad occur in the 
Cretaceous. 
The existing species are numerous, C. madida , mutica , vesper- 
tina, attenuata , sanguinolenta, and stutchburi sp. Reeve, menkei , 
bullata , euglypta , regia , and fumata sp. Hanley, atropurpurea 
Sowerby, bicolor Chemnitz, and virgata Menke, are all referable 
to this subdivision of Cjwtopinna. 
Dr. Charles S. Minot read a paper presenting the results of 
recent investigations on the nervous system, and their bearing 
upon the morphology of the brain. He described : first, the 
development of the ganglia, the origin of the sensory nerve 
fibres from them, and their relations to the sense organs of the 
lateral and epibranchial lines ; second, the differentiation of the 
neuroblasts in the spinal cord and brain and the outgrowth of 
the efferent fibres; third, the relations of the neuromeres, or 
segments of the nervous system, to the nerves, especially in the 
head. 
1 The marks of a few faint scales were observed in a specimen of P. menkei from 
Singapore. 
Puma radiata and tenuistriata Munst., of the Jura are figured with great ac- 
curacy by Goldf. but being apparently young shells it is difficult to place them. 
