DALL: MOLLUSCA AND BRACHIOPODA. 363 
S. solen (mediterranea Lamarck + togata Poli) the chondrophore has no anterior. 
or posterior rib, and the anterior exposure of the internal part of the ligament is 
reduced to a narrow line directed obliquely backward to the upper anterior angle 
of the posterior adductor scar. 
In S. velum Say, the most common species of New England, we find the liga- 
ment has become wholly opisthodetic, no part of it appears in advance of the 
beaks, and there is no exposure in front of the nymphs (or chondrophores) of 
the ligament on the interior surface of the shell. The chondrophore in each 
valve has an anterior and a posterior prop, neither being produced into a rib, and 
the posterior adductor scar is only partly included in the space between the two 
props, the posterior prop touching the middle of the dorsal edge of the scar. In 
S. borealis Totten, the same arrangement prevails, but the props are so strong 
and the nymph so projecting that a small cave under the nymph is created. On 
the anterior edge of the nymph is a small, narrow, elongate, muscular scar which 
may belong to one of the pedal retractors. S. panamensis Dall agrees with 
S. velum, except that the anterior prop is produced along the anterior edge of the 
adductor scar, as a feeble ridge. 
In 8. agassizit Dall there are no supports to the chondrophore and no interior 
exposure of the hgament, which is opisthodetic and wholly external. As far as 
can be judged from the material at hand, there seems to have been a series of 
muscular attachments for a considerable distance along the dorsal margin of the 
valves in front of the supposed pedal protractor scar above referred to. At least 
there are strong radial striations resembling the scar of adhesion of a muscle. 
S. patagonica K. A. Smith (Challenger Report, 1885) has a hinge apparently 
similar to that of S. agassiziz, but in the unique specimen a thickening along the 
dorsal side, which I strongly suspect to be pathological. If this suspicion proves 
correct, it is probable that 8. macrodactyla, which is of four years later date, will 
prove to be synonymous. ) 
The groups into which the species fall, according to their characters, are as 
follows : 
I. Ligament amphidetic, chiefly internal. 
1. Subgenus SoLemya s.s. Ligament exposed internally, in advance of the chon- 
drophore. 
A. Proximal part of the chondrophore prolonged as a thickened ridge part 
way across the interior of the valve . . . . . . S. australis Lam. 
B. Base of the chondrophore divided, anterior part extended as a narrow 
ridge; posterior part forming a thickened prop to the chondrophore. 
S. parkinsonii Gray. 
C. Chondrophore thickened, without props or extended rib. ‘S. solen v. Salis, 
II. Ligament opisthodetic, internal. 
2 Subgenus Perrasma Dall. Ligament not exposed internally in front of the 
chondrophore. 
