Chatwin: Cretaceous Lamellibranchia of Yorkshire. 203 
Other changes in nomenclature may be noted briefly :— 
Isocardia angulata, Phillips (common in the jaculum and 
brunsvicensis-zones of Speeton)=Corbula angulata. Phola- 
domya neocomiensis, Leymerie (from the Lower Cretaceous of 
Speeton)=Panopaa gurgitis (Brongniart). Pholas constricta 
Phillips (same horizon and_ locality)=Martesia constricta. 
Mya _ depressa, Phillips (jaculum-zone, Speeton)= Thracia 
phillipst, Roemer. Mya phaseolina, Phillips, probably belongs 
to the genus Tellina. One new species of Pholadomya, from 
the lateralis, jaculum, and brunsvicensis-zones of Speeton, 
has been established under the name P. speetonensis, Woods. 
The Oysters have received special attention and are pro- 
fusely illustrated in this monograph, but only one Yorkshire 
species is discussed, namely Exogyra sinuata (J. Sowerby) from 
Speeton. In the treatment of other members of the family 
due attention has been paid to the plasticity of the group and 
to the effects of environment. Thus the general tendency has 
been to include under one name forms that have hitherto been 
regarded as separate species. Dr. Rowe (Proc. Geol. Assoc., 
vol. 18, p. 295, 1904) lists four species from the Chalk of York- 
shire, and three of these, O. vesicularis, Lamarck, O. hippo- 
podium, Nilsson, and O. proboscidea, Archiac, must now be 
included under O. vesicularis, Lamarck. The fourth was 
listed as O. wegmanniana, but this species has not been found in 
the English Chalk, O. boucheroni, being the correct name. 
The Inocerami also were studied particularly, and besides 
an exhaustive account in the monograph, a separate paper 
appeared on the evolution of this genus.* Probably no group 
of the Mollusca was in greater need of study than the Inocerami, 
so the wisdom of the Council of the Paleeontographical Society 
in devoting a great number of illustrations to this genus is 
to be appreciated. Many important points were established 
as a result of the complete survey of the group: some species 
were found to occur at definite horizons, transitions between 
species could be traced, and definite factors determined in the 
evolution along certain lines. Thus Inoceramus crippsi 
Mantell (the name has done veteran service in its time by cover- 
ing a multitude of widely different forms) is a species con- 
fined to the Cenomanian, characterising especially the varians- 
zone. Its variety reachensis, Etheridge, is confined to the 
subglobosus-zone. A complete transition can be traced 
through IJnoceramus (no longer Actinoceramus) sulcatus, I. 
concentricus, var. sub-sulcatus, to Inoceramus concentricus, 
and from Inoceramus lamarcki Parkinson to Inoceramus (no 
longer Volviceramus) involutus, J. de C. Sowerby. As definite 
factors in the evolution of the group we may note the angle 
* Quart. Journ. Geol. Soc., 1912, pt. I, pp. I-19. 
1913 Mayt. 
