252 The Anten'cav Geoloyisl. October, ]«95 
Disttihulioa of Sharks tii the CrelaceoKH. C. R. Eastman, Cam- 
bridge, Mass. (Read by title.) 
TemiiinohH/i/ propoHed for Description of Pelectjpoda. Alpheus Hy- 
Ain% Cambridge, Mass. This paper states that the so-ealled hinge of 
bivalves is a general term applicable to the functional part, which as a 
rule is more extensive than the primitive morphic hinge. For the last 
the name cardo is proposed. This occurs in the young of all forms, as 
a rule, in some stage; and it is persistent throughout life in some forms, 
as the Arcidae, most of the Aviculidse, the Ostreidag, and the Pectenidse. 
The cardo is coextensive with the functional hinge in these families and 
some others: but in all the more specialized shells of Pelecyijods it is 
confined in the later stages of growth to the central (amphidetic) or pos- 
terior (opisthodetic) part of the funt'tional hinge area. The mode of 
growth of the anterior dorsal part of the shell shoves the anterior arm 
of the cardo toward the beaks and finally carries this nearly to a line 
between them, or even posterior to them in the opisthodetic forms. 
This area may assume either a crescentic or lunate shajie, or be heart- 
shaped, spear-shaped, or linear. The boundaries are traced by the bands 
of growth that terminate on the borders of this space: and it is, as a 
rule, completely filled by the morphic ligament. This last is often 
longer than the functional ligament, and the term is applied here to the 
whole of the primitively continuous periostracum of the cardo. These 
are the usual senses in which the terms hinge and ligament have been 
used. Dall has proposed "resilium" for the differentiated internal parts 
of the ligament, but has used that term itself for the functional part 
only of that organ, which is often smaller than the periostracum. The 
hinge consists then of the cardo, which includes cardinal line and area, 
and also the internal hinge plate and teeth parts developed dviring the 
evolution of the Pelecypoda, and for these latter the name articulus is 
proposed. The cardo is the fixed jjoint of comparison. This is dorsal 
in most Pelecypoda. but maj' shift to all positions between this and the 
anterior end of the body, as it does in Ostreida?, Aviculid;e, Pectenidae, 
and Trigonia. 
It is proposed that, in descriptions of the exterior of bivalves, paleon- 
tologists and conchologists should systematically describe first the cardo, 
next the articrdus, both as parts of the hinge, and then take up the 
other areas in succession, beginning at either end of the cardo accord- 
ing to the form, preferably perhaps at the anterior end. The parts an- 
terior to the beaks are in the anterior region: the central or innbonal 
region comprises the median and usually more elevated parts: and the 
posterior region, lies behind the beaks in elongated shells, but in those 
with an anterior cardo these regions appear to revolve with the bands of 
growth, becoming in the Aviculida?, PectenidJ^e and Ostreida" quite dis- 
tinct with relation to the beaks. These last and the wings are in the an- 
terior region in these animals, and it becomes necessary to accept differ- 
ent boundaries for the regions. The umbonal elevation is no longer 
transverse but runs antero-posteriorly, and the jjosterior region occupies 
the opposite pole to the cardo, so that it is questionable whether it is 
