THE NAUTILUS. 3 



muscles is, on the contrary, that of closing the valves, and the position 

 of these as related to the position of the compound ligament facilitates 

 exactness in the inter-locking of the hinge teeth. Now these organs 

 or devices for opening and closing the shells are of exceeding promi- 

 nence in S. Nuttallii, and the opportunity for examining a fine series 

 has recently heen afforded me, by the gift of a large number for culi- 

 nary purposes, 1 by Mr. and Mrs. Oldroyd. 



The adductors are exceedingly large for shells of the size and 

 weight, and the ligament being in proportionate size to these muscles, 

 makes this form particularly desirable for the study of these charac- 

 ters. When alive and gaping, the least disturbance will be followed 

 by an energetic closing of the shell, with a snap so vigorous as to 

 cause a chipping or fracture of the vertical edges of the valves. The 

 strength and tenacity of the grip, when the powerful adductors are 

 brought into action, may be easily proven by the insertion of the 

 finger-tips into a partially open shell. 



The texture or substance of the shells in the Saxidomi is less com- 

 pact or solid than in Tivela crossatelloid.es, and the comparative 

 weight of examples of the same dimensions is as 10 to 13; while the 

 mass of the adductors and ligaments are fully twice as large in Saxi- 

 domus as in Tivela, examples of the same size being compared. 



The differences exhibited by these forms, both belonging to the 

 Venerida, indicate differences in habits and environmental conditions, 

 and no doubt others not readily perceived. 



A NEW SPECIES OF SISTRUM. 



BY IIEXRY A. PILSBRY. 



Sistrum nlcocheanum, n. sp. 



Sliell imperforate or rimate, fusiform, thick and strong, brownish 

 flesh-colored, the spiral lira 1 brown. Sculpture of strong, rounded, 

 longitudinal waves equal to their intervals, 8 or 7 in number on the 

 last whorl ; these waves crossed by rather strong spiral cords, which 

 widen into transversely oblong low tubercles upon the summits of 

 the waves. Between these cords there are several spiral threads in 

 most or all of the intervals. Whorls about 5^, convex, the last one 

 with concave outlines below, produced in a rather long anterior 



1 Tbis "clam" makes an exceedingly delicious soup or broth. 



