CLASS GASTROPODA 
289 
SECTION DENDROCHITON Berry, 1911 
Chaetopleura thamnopora Berry, 1911 
Proceedings, Philadelphia Academy of Natural Sciences, 487; text figures 1-7 • PI 40 
Shell small, oblong, rather narrow for Mopalia, much elevated and 
strongly carinated, the side slopes nearly straight. Valves sharply beaked 
in front; the lateral areas fairly well-defined, not raised, having a few very 
faint radial grooves, but without well-marked sutural or diagonal ribs. 
Central areas ornamented with a series of about nine or ten very strong 
low, broad, longitudinal riblets, curved and converging toward the median 
ridge; their intervals of nearly equal breadth, not latticed or otherwise 
sculptured. On the jugal tract these ribs are obsolete or wanting. Entire 
surface minutely granular-porous, but not so distinctly as in M. heathi 
and due largely to the numerous sense organs which under a high power 
appear with great clearness. Anterior valve everywhere very finely granu- 
lous, otherwise without distinct sculpture. Central area of posterior valve 
reduced, but similar in ornamentation to those of the median valves; mucro 
anterior to the middle of the tegmentum; posterior slope steep, slightly 
concave; posterior margin of the tegmentum in general semicircular, but 
rather abruptly (though not extensively) squarish truncate or emarginate 
at the middle. Anterior valve with 7 slits; intermediate valves with 1-1 
slits; tail valve “ischnoid,” with a regular crescentic insertion plate cut 
by 6 slits. Sinus broad, rather shallow; in last valve narrower and minutely 
crenulate. No median sinus behind, and no indications of an approach to 
this condition other than the above-noted squaring of the tegmentum. 
Girdle narrow, apparently nude even under a hand lens, but shown by high 
power to be well-clothed above with numerous exceedingly minute, but not 
very crowded, ovid spicules developed into stout elongate spines at the 
margin. The spinelets of the lower surface are longer, flatter, and more 
pointed than those of the upper, being somewhat intermediate in character 
between these and the marginal ones. Opposite each suture is a pore from 
which springs a group of about 6 recurved bristle-like hairs surrounding a 
single much larger and longer bristle, which branches freely, and in living 
or alcoholic material is a prominent feature even to the unaided eye. Being 
very brittle, these structures are frequently broken off, but their stumps or 
pores are always evident and show a very regular arrangement. Apparently 
homologous with the sutural tufts are two similar ones on each side of 
the head valve, one on each side of the tail valve, and one in the median 
line in front and behind. In addition there is a second series of much 
smaller but equally distinct tufts lying just outside of the first and in a 
more or less regular alternation with them. The long central bristles have 
[891] 
