MUSEUM OF COMPAKATIVE ZOOLOGY. 253 



Section SATURNIA Seguenza. 



Leda (Saturnia) pusio Philippi. 



Nucula pusio Phil., Moll. Sic, II. p. 47, pi. xv. fig. 5, 1844. 

 Leda pusio Jeffreys, P. 2. S., 1879, p. 578. 



Two specimens exactly agreeing with Jeffreys and Seguenza's specimens 

 were dredged dead at Station 236, near Bequia, in 1591 fnis. 



This species has a gap in the tooth line, but no internal ligament. There is 

 a pit under the beaks, exterior to the line of the teeth, which may have had a 

 ligament in it. Mediterranean specimens show the same. Seguenza places it 

 in his section Saturnia as type. There is a gradual change from shells with 

 an internal cartilage set in a spoon-shaped process, and an outside ligament, to 

 those where the two seem to have come together, coalesced, and finally become 

 entirely external. It does not seem possible to draw hard and fast lines. 

 Yoldia and Malletia, Leda and Tindaria, approach each other by insensible, or 

 rather undefinable degrees. The extremes of the series are very distinct, the 

 passage from one to the other very gradual. I do not regard any of the divis- 

 ions of Leda as more than sectional ; at least, until more is known about the 

 soft parts, I prefer to regard them so. 



Others may be able to decide definitely what constitutes a genus, a subgenus, 

 or a section, and measure all these groups by that standard. I find myself 

 unable to do more than point out relative values, as they appear to me, in a 

 single series, and even in this I find it often difficult to satisfy myself that the 

 correct proportion between them has been attained. 



Leda (Saturnia) quadrangularis Dall. 



ILeda (Jeffreysi Hidalgo, var. ?) qnadrannularis Dall, Bull. M. C. Z., IX. p. 124, 1881. 



Plate VIII. Fig. 6. 



Habitat. Station 33, 1568 fms. 



This turns out on comparison with specimens to be entirely unlike L. Jef- 

 frey.ii, and I have not found anything like it. It is nearest pusio, and has the 

 same concentrically finely undulate surface, but the basal pout and longest 

 slope of hinge-line are posterior here, while, in pusio, both are anterior. I 

 have not been able to satisfy myself that there was any ligament pit inside. 

 There is a smooth interval between the two sets of teeth, but no pit, and no 

 evidence that any ligament was attached there. It would belong to Seguenza's 

 section Saturnia. The valve is 4.6 mm. in length, 4.0 mm. high, and the pair 

 were probably 3.0 mm. in diameter. 



