156 Cnck : A Rare Fun-m of Actiuocamax [A. Grossouvrci). 



it has its least diameter ; from this level up to the border of the 

 aheolus it enlarg-es slightly. 



None of M. Janet's specimens showed the ventral fissure 

 quite clearly. They exhibited only a slii^ht indentation of the 

 border of the alveolus proloni>^ed or not by a very slight and 

 very short groove. 



The dorso-lateral grooves are not very deep, but wide and 

 distinct, and extend over more than three-fourths of the length 

 of the guard. 



The alveolus was preserved in only two of M. Janet's 

 specimens. In one it was moderately deep, and its surface 

 rendered irregular by radiating ridges ; in the other it was very 

 smooth, without radiating stride or concentric ridges, onl)' very 

 slightly excavated, and with a small but distinct pit in the 

 centre. 



The surface of the guard is smooth and without any granula- 

 tion, ' but,' says M. Janet, ' the superficial layers have been, 

 peeled off especially at the lower part of the ventral surface, so 

 that near the extremit}- there is seen to appear the very oblique 

 section of the concentric layers nearest the apical axis. The 

 base of a coral which remains attached to one of our specimens 

 proves that this alteration is not recent, and is due without 

 doubt to the fact that in this part of the guard, as in the 

 neighbourhood of the alveolus, calcification was less than in 

 other parts.' 



'This alteration,' continues M. Janet, 'has caused to dis- 

 appear, if howexer it ever existed, the mucronated point so 

 clear in Belemnilella mucronata^ Aciinocamax ffnniii/d/us, and 

 Actiuocamax subventricosus. ' 



Mr. Mortimer's specimen (PI. XVI., figs. 1-4) agrees very 

 closely with M. Janet's largest example. For the sake of 

 comparison, the dimensions of these two specimens are given 

 in the following table ; the English specimen is obviously, how- 

 ever, more incomplete anteriorly then the French example, 

 because it presents no indication of the alveolus, and appears 

 therefore to be somewhat shorter, although the other dimen- 

 sions are almost the same. 



I-<nt^tli ill inillimclres 



W'litro-dorsal diameter at the most inflated part 

 Transverse diameter at the most inflated part ... 

 X'enlro-dorsal diameter at tlic narrowest jiart, 



/.('., at tile anterior end 

 Transverse diameter at the narrowest pai-t, /.<■., 



at the anterior end ... 



