BALL: MOLLUSCA AND BRACHIOPODA. 365 



Solemya (Acharax) agassizii Dall. n. sp. 



Plate 16, figure 10. 



Shell large, elongated, heavy, chalky, with a strong blackish periostracum 

 which, except near the middle of the base, is produced into long ragged processes 

 beyond the margin of the valve ; the surface of the valve is radially channelled 

 with wide, deep channels which are reflected by prominent ribs on the inner sur- 

 face of the valves ; it is the portion of the periostracum which lies in the channels 

 which forms the processes, and that which covers tlie interspaces which fails to 

 retain its continuity except for a short distance beyond the edge of the valve ; 

 valves very inequilateral, posterior end very short, hinge line nearly straight, the 

 sulcus for the ligament nearly parallel with the hinge line, and the nymph incon- 

 spicuous so that on a casual glance one might suppose there was none; beaks 

 not raised, the hinge line below them thickened and flat, radially striated ; anterior 

 hinge line straight, thin ; valves widest at the anterior margin ; anterior part of 

 the valve with six or seven strong radial channels, the interspaces wider, and often 

 with their margins a little raised or with a sliglitly elevated border ; beyond the 

 channelled area there are a few faint radial furrows and a perfectly smooth un- 

 furrowed space in the middle of the valve ; posterior slope straight, furrow for the 

 ligament long, deep, and wholly external ; there is a wide triangular smooth space, 

 in front of which are five or six channels radiating to the margin, much more shal- 

 low than those at the anterior end and defined chiefly by shallow furrows at each 

 side of the obsolete channel and the raised margins of the wide interspaces ; interior 

 chalky, the anterior muscular impression feeble, the posterior stronger and ovate. 

 Length of the valve, excluding periostracum, about 95 ; height, 30 ; and diameter, 

 25 mm. The species reaches a length of more than 150 mm. 



U. S. S. "Albatross," station 3360, Gulf of Panama, in 1672 fathoms, sand, 

 bottom temperature 36°.4 F. U. S. N. Mus. 106,SS5. Also at station 3381, iu 

 1772 fathoms ; 3382, iu 1793 fathoms ; 3399, in 1740 fathoms ; 3434, in 1588 

 fathoms ; and 4654, off Aguja Point, Peru, iu 1036 fathoms, all on soft bottom 

 with temperatures varying from 35°.8 to 37°. 3. The range of the species, so far 

 as known, extends from the Gulf of California south to the vicinity of Aguja 

 Point, Peru. 



Owing to the burrowing habit of the genus, only fragments and dead valves 

 were obtained in the trawl. 



This species belongs to the group of S. macrodactyla Rochebrune and Mabille, 

 from Orange Harbor, Patagonia, but differs from it in the smooth middle area of 

 the valves, proportionately shorter posterior end, and much larger size. It is the 

 largest species I have seen in which the ligament is wholly external, or iu which 

 the shell is so solid as to survive the loss of the tough protective periostracum. 

 S. grandis is a shorter and wider species. The young of S. agassizii are more 

 cylindrical than the specimens of S. macrodadi/la of equal size. 



When first collected this species was confounded with the Solemya johmoni 

 Dall, a northern species described from a specimen collected off the coast of Ore- 



