92 MK, G. C. CBICK ON THE MUSCULAR ATTACHMENT OF THE 



following dimensions : — diameter 120 mm. ; width of umbilicus 49 mm. ; height of 

 outer whorl 44 mm. ; greatest thickness of ditto 41 mm. The posterior portion of the 

 body-chamber is preserved ; one side is much crushed, but the rest is fairly comjilete. A 

 portion of the test still adheres to the cast. The sjjecimen, measured along the median 

 line of the periphery, is 165 mm. long ; its transverse section is ovate, the greatest 

 thickness being at about two-fifths of the height of the whorl from the inner edge ; at 

 its posterior end the height of the whorl and its thickness (allowing for the crushing) are 

 80 mm. and 27 mm. respectively. The impression of one shell-muscle is well shown, 

 but only the inner portion of the other (PI. 19. figs. 11, 12). The whorl is very slightly 

 imj^yressed by the preceding whorl. In shape the impression is truncated-oval, its 

 longer diameter being transverse and tlie truncated end towards the median line of the 

 dorsal surface. Arising a little in advance of the saddle on the side of the antisiphonal 

 lobe, the boundary of the impression passes forward for about 5 mm. nearly parallel to 

 the median line of the dorsal or antisiphonal surface, and at 1'5 mm. from its fellow on 

 the opposite side ; then, curving outward, it extends for about 10 mm. ia a direction 

 almost at right angles to its previous course; bending rather abruptly backward, it 

 jiasses for a short distance nearly parallel to the boundary of the impressed zone ; tehn, 

 curving inwai'd and backward, it speedily disappears. The greatest width (transverse) 

 of the impression is 12 mm. There is no trace of the annulus. The boundary of the 

 impression is indicated by a depressed line, Avhich is rather deejily incised on the inner 

 and outer portions, but somewhat less so on the anterior portion. The portion of the 

 surface of the cast bounded by tlie impression is a little rouglier than the rest. Owing 

 to the crushed condition of the whorl, only the inner portion of the other impression 

 is preserved. The impression is so situated that in a lateral aspect of the whorl only a 

 very small portion of it can be seen (fig. 12). 



Lytoceras qiuidrisulcatimi, d'Orbigny, sp. — One example of this species, collected by 

 Dr. J. W. Gregory in East Africa, exhibits a portion of the muscular impressions. It is 

 a crushed fragment of a natural cast of the posterior pai"t of the l)ody-chamber. The 

 inner portion of the whorl is badly crushed, but exhibits on either side a part of the 

 muscular scar. At the base of the body-chamber the whorl is 30'5 mm. high and 

 80 mm. thick, the greatest thickness being a little within the central portion of the lateral 

 area ; tlie transverse section is therefore nearly circular. The muscular scars are somewhat 

 darker than the surrounding surface of the cast, and present a slightly roughened 

 appearance. That on the left is the better shown, but its inner portion is obscured so 

 that the "whole of its anterior border is not visible. Its bovmdary is usually a feebly- 

 indented line, but sometimes a slightly-raised line. Tiie anterior boundary of this 

 impression appears to commence at about 7'5 mm. in advance of the most anterior part 

 of the last septum, and about 8 ram. from the central line of the impressed zone; it 

 passes thence slightly forward and outw^ard for a distance of about 2 mm. ; then, 

 curving backward at about 10*5 mm. from the median line, it passes for a short distance 

 nearly parallel to the median line ; then, at about 4'5 mm. in advance of the last septum, 



