BATHYPELAGIC SQUID BATHYTEUTHIS 39 



ens on the lamellae. The rostrum of the upper beak is curved and 

 sharply pointed; the curved jaw angle has a slight protuberance. The 

 insertion plate of the palatine lamella is nearly two times longer than 

 high and the posterior end is angled. The rostrum of the lower beak 

 is relatively blunt and forms nearly a right angle with the long, nar- 

 row rostral lamella. The gular lamella is broad; it is bluntly rounded 

 posteriorly. 



The radula consists of seven transverse rows of pointed teeth and 

 two rows of elongate lateral plates (pi. 3f). The rhachidian has a 

 broad, low base; the median cusp is moderately long and bluntly 

 pointed. No lateral cusps exist, but the basal, concave, lateral borders 

 of the rhachidian are often set with irregular protuberances. Some of 

 these may approach the size of lateral cusps, but still they remain as 

 protuberances and are not cusps. The first lateral teeth are broadly 

 crescent-shaped with convex medial and concave lateral borders; the 

 blunt cusp is about as long as that of the rhachidian. The second lat- 

 erals are long, slender and crescent-shaped; the cusps are slightly 

 longer and more pointed than the first laterals or the rhachidian. 

 The basal lateral borders of the first and second lateral teetli are also 

 marked with slight irregularities or small protuberances, but these are 

 not incipient cusps. The third lateral teeth are very long, slender, 

 scythe-shaped ; they terminate in moderately sharp points. The lateral 

 plaques are elongate plates set on the radula ribbon at about 45° to 

 the long axis of the radula. The long sides are concave and the ends 

 are bluntly rounded. In other specimens the plates become very knobby 

 or irregular, or they may even be divided into two or more small 

 masses. 



The gladius is embedded in the inner surface of the mantle wall. 

 The circular muscles of the mantle are continuous over the gladius 

 so that it is not visible in the dorsal midline. The anterior end of the 

 rhachis lies on the inner surface of the mantle covered only by a thin 

 sheath. At its anterior tip the rhachis is covered by a thin cartilaginous 

 band. This band and the exposed rhachis posterior to it make up the 

 mantle component of the mantle-nuchal locking apparatus. Immedi- 

 ately posterior to the nuchal locking apparatus the gladius is bound to 

 the inner surface of the mantle wall by a strong, thick muscle that is 

 an extension of the inner portion of the collar muscle. This sheath 

 spreads posteriorly and ventrally and envelops the liver in a strong 

 muscular sheath. The strong dorsoanterior band is continuous ventral 

 to the mantle, but it diminishes posteriorly, so that the fibers of the 

 liver sheath attach to the shell-sac along the lateral edges of the 

 rhachis. The remainder of the gladius is visible in the shell-sac pos- 

 teriorly extending from the heavy muscle band to the termination. 



