212 BULLETIN OF THE 
a specimen dredged by Pourtales in the Straits of Florida, now in the National 
Museum, and was only magnified some two and a half times, linear. From 
among the forms at first confounded under the name of lucidum, and several 
of which have been carefully worked out by Mr. Edgar A. Smith of the British 
Museum in the Challenger Report, the following may be discriminated :— 
1. P. lucidum (Jeffr. em.) Smith. Fig. “a” of 1873, E. Atlantic. 
2. P. Pourtalesianum Dall. Fig. “b” of 1873, West Indian region. 
3. P. meridionale Smith 1. c. (A. lucidum Jefir., var. striata Jeffr., according 
to localities and specimens cited P. Z. S., 1879, p. 562). 
2a. P. Pourtalestanum, var. striatulum Dall (agrees with Jeffreys’ descrip- 
tion of his var. striata, but not with his specimens). 
2b. P. Pourtalesianum, var. marmoratum Dall. West Indian region. 
Mr. Smith has discriminated the typical P. lucidum (Chall. Rep. Lamellibr., 
p- 317, pl. xxiv. figs. 2 a-c), from which the form here called Pourtalesitanwm 
differs in being more oblique, longer, and of larger size when adult. The 
series of A. Dalli Smith, obtained by the “ Blake,” indicate that A. meridionale 
Smith is possibly the young of Dalli, as the differences of gape and of sculpture 
correspond fairly well to stages of growth observed in the Blake series. Mr. 
Smith, however, is confident that it is distinct. It is at all events perfectly 
distinct from lucidum. My impression is that Dr. Jeffreys derived his idea 
of his variety striata from specimens of 4. Pourtalesianum, var. striatulum Dall, 
sent him by Pourtalés ; but that when he came to describe it he cited Chal- 
lenger localities and specimens, which on a cursory examination he took to be 
the same thing, and omitted to mention his West Indian ones. However this 
may be, the var. striatulum above mentioned agrees perfectly with Dr. Jeffreys’ 
rather brief description. 
No specimens of the typical A. lucidum were obtained by the “ Blake,” or 
have been received from the Fish Commission dredgings on the American or 
Gulf coasts. 
The A. Pourtalesianum,var. striatulum,was obtained by the “ Blake” at Station 
128, near Frederikstadt, in 180 fms.; Station 192, off Dominica, in 138 fms.; 
and Station 226, off St. Vincents, in 424 fms. The bottom temperature at 
these stations varied from 42°.5 to 64°.0 F. 
The variety marmoratum (Dall, Bull. M. C. Z., IX. p. 117, 1881), with its 
brilliant mottling of orange, scarlet, brown, bright yellow, and opaque white 
dots or flecks, appeared indifferently at most of the stations in company with 
the pale translucent typical form. 
I have examined one hundred and forty valves of this species, 64 per cent of 
which had ten internal ribs; 5.7 per cent nine ribs ; and 21.5 per cent eleven 
ribs ; not counting the crural callosities. Six specimens had twelve ribs, and 
one each had eight, thirteen, fourteen, fifteen, and twenty-one ribs. The extra 
ribs usually appear as intercalary knobs or lire near the outer edge of the 
ribbed area, and seldom extend into the body of the shell like the normal 
ones, 
