L. Boss—Tail of Comet b, 1881. 303 
Diplodonta turgida Verrill and Smith, sp. nov. 
ell large for the genus, round-ovate, a little longer than 
high, very swollen; the two ends nearly equally rounded, the 
anterior a little narrower; ventral edge broadly and regularly 
rounded; beaks nearly central, somewhat forward of the mid- 
dle, strongly curved inward and forward, acute. Surface with- 
out sculpture, smooth except for the evident lines of growth. 
In the right valve there are, opposite the beak, two nearly equal, 
stout, sharp teeth, separated by a space of about the same 
width; back of these, and partly joined at base to the posterior 
one, there is a much larger, broad, stout, obtuse tooth, with a 
groove on its dorsal side; external cartilage-groove and _ its 
lamella are long and narrow, curved. Length, 29™; height 
(umbos to ventral edge), 25™"; breadth, 23™™. 
Station 950; 69 fathoms. One right valve. 
Art. KLII.—WNote on the Tail of Comet b, 1881; by Lewis 
Boss. With Plates V and VL. 
and unexpected moved me to prepare some rude sketches of 
the tail, with brief notes as to its position in thes rom 
several cau opportunities for ng such studies 
€. 
€ engravings (Plate V), accompanying this paper were 
reduced from drawings compiled from the original sketches 
and notes, 
_ These were made in the open air at the times of observation 
indicated. In all cases the chief object of interest was what 
may be conveniently termed the right-line tail, which was far 
more conspicuous than the other branch on June 26, scarcely 
perceptible on June 28, and entirely wanting on July 1. Itis 
to be regretted that on these dates charts were not used in the 
preparation of the original sketches, except for reference. The 
final drawings were laid down on copies of Schwinck’s polar 
