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 Keport, the following may be discriminated : — 



1. P. lucidum (Jeflfr. em.) Smith. Fig. "a" of 1873, E. Atlantic. 



2. P. Pourtalcsianum Dall. Fig. " b " of 1873, West Indian region. 



3. P. meridionale Smith 1. c. {A. Iv^idumJeSi., var. striata Jeffr., according 

 to localities and specimens cited P. Z. S., 1879, p. 562). 



2 a. P. Pourtalesianum, var. striatulum Dall (agrees with Jeffreys' descrip- 

 tion of his var. striata, but not with his specimens). 



2 b. P. Pourtalesianum, var. mxirTnoratum Dall. West Indian region. 



Mr. Smith has discriminated the typical P. lucidum (Chall. Rep. Lamellibr., 

 p. 317, pi. xxiv. figs. 2 a-c), from which the form here called Pourtalesianum 

 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 diflerences 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 J. Pourtalesianum, var. striatulum Dall, 

 sent him by Pourtales ; 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,yaT. striatulum,v!-as 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°. 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 haA'e 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 lirse near the outer edge of the 

 ribbed area, and seldom extend into the body of the shell like the normal 

 ones. 



