MUSEUM OF COMPARATIVE ZOOLOGY. 211 



applied to the internal surface of the upper valve, thus forming in the adult 

 and perfect shell a concave area about the distal margin of the inferior valve. 

 Type Amusium fenestratum Forbes. 



The species of this section are found in deep waters, -widely distributed, 

 except in the arctic seas. It should be noted that in this group, as in many 

 other Pectens, there are often a pair of ridges or lirse, sometimes very promi- 

 nently elevated, on the inside, nearly parallel with the margin of the body 

 of the valve and situated at or on the prominence inside which is adjacent 

 to the auricular sulcus outside. These are not peculiar to either section of 

 Amusium, and are not counted by me in enumerating the internal lirse of 

 species of Propeamitsium. I notice that Smith in the Challenger Report has 

 counted them as lirse; so in the same species, when they are present, the num- 

 ber of lirse by my enumeration would always be two less than his. I have 

 called them the auricular crura for distinction's sake. They are found in 

 species of Pseudaviusium as well as of Propeaviusium proper, and are some- 

 times absent in species of either group. 



Amusium (Propeamusium) Pourtalesianum Dall. 



Amiisshim lucidum Dall, Bull. M. C. Z., IX. p. 117, 1881. 



< Pleuronectia lucida Jeffr., Depths of the Sea, p. 464, fig. 78 b, 1873. 



<.Amussium lucidum Jeffr., Ann. Mag. Xat. Hist., XVIII. p. 425, Xov. 1876 ; P. Z. S., 



1879, p. 562. E. A. Smith, Challenger Rep. Lamellibranchs, p. 317, pi. xxiv. 



figs. 2 a-c. 



Plate IV. Fig. 3. Plate V. Figr. 13. 



Taken at Station 2, off Morro Light, in 805 fms.; Station 5, in 229 fms. ; Sta- 

 tion 19, in 310 fms. ; Station 21, in 287 fms. ; Station 35, in 804 fms. ; Station 

 44, in 539 fms.; all in the Gulf of Me.xico near Cuba. Also in the Gulf west of 

 Florida in 30 fms., and at Charlotte Harbor, "West Florida, living in 13 fms.; 

 Station 47, in 337 fms.; Stations 50, 60, and 100, off Havana, in 119, 480, and 

 400 fms.; Stations 162, 163, and 167, near Guadalupe, in 734, 878, and 175 

 fms.; Stations 176 and 177, near Dominica, in 391 and 118 fms. ; at Barbados, 

 in 100 and 154 fms.; Station 227, near St. Vincent, in 573 fms.; station 262, 

 in 92 fms., near Grenada. The depth at winch it has been found living varies 

 from 805 to 13 fms., aud the bottom temperature from 39°. 5 F. to 82°. 5 F. 

 This is a remarkable range. 



Tliis species was included under the name of lucidum by Dr. Jeffreys in 

 1876, and had been well figured in 1873. The figures " a " and " b " of luci- 

 dum represent what are now considered as two different forms. At that early 

 date in deep-sea work, minute discrinunation as to species was less practicable, 

 and therefore less usual, than at present, when the amount of material is so 

 much greater. 



Figure " a " of the " Depths of the Sea " is magnified ne{jrly four times 

 linear, and comes from the Eastern Atlantic. The other figure was taken from 



