CRICK : APEKTURE OF A EACULITE. 79 



more pronoiinccd towards the anterior portion ; the anterior side 

 of each is steep and only 1-5 mm. in length, but the posterior side is 

 feebly inclined to the longitudinal axis and is about 4 mm. in length. 

 In passing round to the sides these folds curve gently backwards, and 

 gradually disappear at about the centre of the lateral area. With the 

 exception of the anterior one, these folds pass uninterruptedly over 

 the siphonal area. The anterior fold is, however, flattened at the 

 middle of the siphonal area, and passes laterally on to the everted 

 margin of the aperture. A yet more feeble ridge or fold arises on 

 either side of the median portion of the anterior spout-like projection, 

 and passes round, over the lateral area, parallel to the other folds, to 

 the margin of the aperture. 



On the antisiphonal area immediately behind the aperture there 

 is a constriction about 4 mm. wide, having its greatest depth (1 mm.) 

 close under the margin of the aperture ; in passing round to the sides, 

 this is only about 2 mm. wide, and keeping close to the margin reaches 

 across about one-third of the lateral area. 



The margin of the aperture is not quite perfect ; but where one 

 side is incomplete, the other side, fortunately, is well preserved, so 

 that by a comparison of the two sides, the original form of the entii'e 

 margin can be ascertained. On the antisiphonal and lateral areas 

 the margin is somewhat thickened and everted. In the central line 

 of the antisiphonal area, the margin projects slightly forwards and 

 outwards, forming a blunt antisiphonal apophysis about 1 mm. long. 

 Starting from this apophysis, the margin, as seen in a lateral aspect, 

 first curves backwards and towards the siphonal side, over about one- 

 third of the width of the lateral area ; then, after passing forwards 

 with but a slight inclination to the longitudinal axis of the shell, 

 it forms a broad curve having its convexity towards the siphonal 

 side, the deepest part of the curve being at about the middle of the 

 lateral area ; then, having curved towards the antisiphonal area to 

 a point distant from that area about one-third of the ventro-dorsal 

 diameter, the margin curves somewhat abruptly towards the siphonal 

 side to meet the most anterior projecting portion of the siphonal area. 

 The lateral lappet thus formed is separated from the corresponding 

 lappet on the opposite side by a narrow horseshoe-shaped sinus 

 4"5 mm. wide. 



The principal difference between this specimen and those previously 

 figured consists in the prolongation of the siphonal margin of the 

 aperture into a spout-like projection. 



An examination of Sowerby's figured specimen, now in tlie British 

 Museum Collection (No. 44,005), shows that the anterior extremity is 

 abraded, so that if any spout-like projection were originally present, 

 it has been broken off. Noetling's figiire is so similar to Sowerby's 

 that it is not at all improbable the lack of any such projection in 

 his specimen may be due to the same cause. 



The projection indicates the position of the funnel. Its relative 

 smallness, and therefore the smallness also of the latter, indicate an 

 animal with crawling rather than free-swimming habits. In the case 

 of such an animal with a long (and in the adult, straight) shell, when 



