90 MR. G. C. CRICK 0]S THE MUSCULAR ATTACHMENT OF THE 



line, passes outward and backward in a curve, which nearly meets the last septum at 

 about ll'Onim. from the suture, and thus encloses a subtriangular area on the inner side 

 of the base of the body-chamber. Just before this outer line reaches the last septum it 

 gives off a very faint branch which passes outward towards the periphery, but can be 

 traced for a very short distance only. This is, without doubt, an indication of the anterior 

 boundary of a portion of the annulus. Within and parallel to the outer boundary of 

 the impression there are one or two very faintly indented lines. 



TissoTiA, Douville. 



Tissotia Uwaldi, v. Buch, sj). — The muscular impression is shown iu an example of 

 this species in the British Museum Collection (No. C. 4810 a) from the Chalk (Senonian) 

 of Mezab-el-Mesai, Algeria (PI. 18. fig. 11). The specimen is a natural cast, 8S'5 mm. in 

 diameter ; rather more than one-fourth of the outer whorl is occupied by a portion of the 

 body-chaml)er, but this latter is somewhat imperfect on one side, so that the dimensions 

 of the specimen can best be taken at the base of the body-chamber. Here its dimensions 

 are as follows : — diameter of shell 84'5 mm. ; width of umbilicus 8'5 mm. ; height of outer 

 whorl 42 mm. ; greatest thickness of same (at a short distance from the umbilicus) 47 mm. 

 The whorl is obtusely cordate in transverse section, rather wider than high, and indented 

 to rather more than one-half of its height by the preceding whorl. The anterior border 

 of the muscular impression is represented by a feebly-incised line. It cannot be traced 

 quite as far as the suture of the shell, but on the narrow inner area of the whorl it is 4 mm. 

 from the last septum ; passing thence forward and outward on to the lateral area, it 

 attains its greatest distance from the last septum (viz. 8"5 mm.) at 4 mm. from the edge 

 of the whorl. Then, curving backward, it passes on the vimbilical side of, and at a 

 distance of 1'5 mm. from, the first (counting from the umbilicus) large lateral saddle, and, 

 turning forward, sweeps round in an anteriorly-concave curve immediately about the 

 small saddles occupying the margin of the umbilicus and soon disappears. The muscular 

 scar thus bounded appears to have been an oval about 10 mm. by 7 mm., its longer axis 

 being placed nearly in a radial direction but slightly inclined backward. Prom the 

 anterior portion of the boundary of this impression a feebly-depressed line passes 

 backward and outward in a broad f or wardly- convex curve to within about 2*5 mm. of 

 the outer portion of the first (counting from the umbilicus) large lateral saddle, then in 

 a forwardly-concave curve crosses the adjacent lobe, and disappears just above the next 

 lateral saddle. This line may indicate a portion of the anterior boundary of the 

 annulus. 



The opposite side of the body-chamber has been so much eroded that the muscular 

 impression is not preserved. 



