200 BULLETIN OF THE 
.Terebratula Bartletti Dat. 
Terebratula Bartletti Dall, Am. Nat., Nov. 1882, p. 885. 
Plate VI. Figs. 4 a-c. 
Shell whitish or often with a delicate madder-brown tinge, moderately thin, 
ovoid, inflated, polished, with occasional traces of delicate evanescent ex- 
tremely fine radiating lines, especially on the sides near the hinge line ; apex 
of the neural valve rather attenuated, curving over and closely appressed to 
the apex of the hemal valve ; foramen complete, small, its lower margin pro- 
duced into a sharp point lying over the apex of the hemal valve and conceal- 
ing it; area short, very wide, triangular, bounded by a sharp carina on each 
side, concave, with a median slightly impressed line, posterior margin a little 
arched in a posterior direction; it is entirely concealed in the living shell, 
being as before mentioned closely appressed to the outer surface of the other 
valve; cardinal border rather pointedly arched, teeth small but stout; margin 
of the valve smooth, flexuous ; it falls away a little from a point immediately 
in front of the teeth, then continuing forward is emarginated and its front 
border strongly squarely produced upward and forming two well-marked 
corners between which the front margin is nearly straight ; outer surface of 
the valve roundly convex. Hzemal valve with the margin correspondingly 
flexuous, generally rounded but with a more or less obtuse ridge extending 
toward the beak from the inner angles of the anterior flexuosity: beak rather 
pointed, incurved cardinal process small, semicircular, fimbriated in all cases, 
showing six to eight anteriorly pointing irregular denticulations ; cardinal 
plate divided, its lateral platforms wide, deeply concave ; tooth sockets small, 
narrow, close to the margin of the beak; loop large, very square, curved up- 
ward, proportionally wider and shorter than in 7. cubensis, with a less convex- 
ity in the median line, and without the lateral notches and median prominence 
of T. cubensis. Interior of valves smooth except for the muscular impressions 
and certain ridges due to their changes in the development of the individual ; 
in the hemal valve there is an obtuse ridge (seen through the shell it resem- 
bles a septum as in Waldheimia) between the abductor scars, in the neural 
valve there is a well-marked groove in the same place : in T. cubensis the ante- 
rior margin of the adductor scars is underneath and behind the anterior margin 
of the loop ; in this species (as in T. vitrea) they are considerably in advance 
of it, a circumstance resulting from the greater bulk of the soft parts in the 
latter species, compared with the size of the shell. The measurements in an 
adult individual are as follows. Lon. of neural valve 40.0, of hemal do. 38.0, 
lat. 31.5, lat. of anterior flexuosity 22.0; beak to anterior edge of loop 8.0, to 
points of crura 5.5, width of anterior margin of loop 6.5; diameter 26.75 mm. 
The greatest width of the shell is behind its middle in T. vitrea, as already 
pointed out by me (Bull. Mus. Comp. Zodl., III. No. 1, p. 3, 1871); in the 
present species it is anterior to the middle of the shell. 
