200 BULLETIN OF THE 



Terebratxila Bartletti Dall. 



Terebratula Bartletti Dall, Am. Nat., Nov. 1882, p. 885. 



Plato TI. F1k8< 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 haemal valve ; foramen complete, small, its lower margin pro- 

 duced into a sharp point lying over the apex of the haemal 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 

 comers between which the front margin is nearly straight ; outer surface of 

 the valve roundly convex. Haemal 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 T. cubensisy 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 haemal 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 bi;lk 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 haemal 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. Zobl., III. No. 1, p. 3, 1871) ; in the 

 present species it is anterior to the middle of the shell. 



