ised BULLETIN OF THE 
structure barely visible on extreme of the left valve only; interior of adult 
marked by a flat thickened margination, especially in the left valve, extending 
parallel with the basal margin ; auricular crura elevated into a low ridge or 
blunt tooth on each side; hinge margin furnished with a lanceolate area on 
each side of the cartilage pit which is finely deeply closely grooved in a direc- 
tion vertical to the hinge-line, the projections between the grooves interlock- 
ing so strongly as to cause the hinge-line of one valve sometimes to break off 
bodily, rather than separate from the opposite valve, when one is trying to 
open a pair, even when the soft parts are absent. The shell is prettily varie- 
gated with mottlings of red, brown, and yellow on a creamy ground, both 
valves participating, but the upper one rather the brighter in most cases. 
Alt. 8.5; lon. 9.0; max. diam. 2.0 mm. 
This shell has been dredged by Professor Verrill in 80 to 317 fms. off 
Martha’s Vineyard. Specimens were obtained by Sigsbee off Havana in 450 
fms., and at Station 36 in 84 fms. 
The figure on Plate VI. fig. 5, representing the interior of the voung fry 
of Janira hemicyclica, equally well represents the very young of this species, 
which at this stage can hardly be distinguished from the other except by the 
external sculpture, which is often absent, or by the rugee of the hinge. 
Because the internal lire occasionally fail, or are late in being deposited in 
certain individuals of Propeamusium, Dr. Jeffreys formed the opinion that they 
were of no importance as a specific character. In this manner he was led into 
several errors, from judging merely by the exterior of some of these small shells. 
In the present case the external sculpture is much like that of Amusiwm fenes- 
tratum Forbes, but finer and more regular. Both have similar varieties of 
color. Dr. Jeffreys was thus led to unite them, although they belong to differ- 
ent sections of the genus, as also in the case of A. Hoskynsit and Pseudamusium 
pustulosum Verrill, an error entailing some serious results in the matter of areal 
distribution. Professor Verrill followed Dr. Jeffreys until a special study of 
the group enabled me to call his attention to the discrepancies existing between 
the two species. 
The peculiar arrangement of grooved and corrugated areas on the hinge-line 
is of interest in connection with the development of hinge characters. It is 
very common in the fry of various Pectens. It is well developed in the very 
young P. magellanicus. I have found traces of it in many of the minute 
specimens of Pecten I have examined, though often very faint, and in very few 
does it reach the development attained in the present species. It was the adult 
and permanent characteristic of the extinct genus Neithea, and traces of it are 
even recognizable in some species of Janira or Pecten in their adult condition. 
When I first discovered it in the present species, I naturally supposed I had 
come upon the type of a new generic division, but I have since found it in the 
young of Pectens of nearly all sections of the genus in its widest sense. On 
the other hand, in some species even the very young have hardly a trace 
of it. 
