25 



though obtusely bicarinatc on tlie periphery, and oljsoletel}' keeled at 

 the sides. With the increase of g-rowth the keels diisappear, and the 

 whorls become more rounded, until tinally the last one assumes a sub- 

 quadrangular aspect. The inner half of the sides of the body whorl is 

 compressed, the outer half curves convexly and rather obliquely towards 

 the periphery, which is broad and flattened. The umbilical face of this 

 volution is squarely as well as very deeply truncate, and forms a blunted 

 but ncai'ly right angle with the sides. In the last whorl but one, the 

 umbilical lace is not straight, but slightly convex, and the angle 

 between it and the sides is rounded otf. All the specimens are so much 

 distorted that it is difficult to estimate the jwoportionate width of the 

 umbilicus with much accuracy, but in the example represented on Plate 

 III., which is not fully grown, it is about one-third of the greatest dia- 

 meter. In the adult the last Avhorl increases very much in height, so 

 that the umbilicus may then be rather smaller in j^i'oportion to the 

 shell. The aperture is transversely subquadrangular, the outer angles 

 being broadl}' rounded ; its height is rather less than its breadth, and 

 the emargination of the base is not very deep. 



Tlie sculpture consists of bi-oad, but not acute, raised ribs, and these 

 are ornamented with tubercles, some of which originally bore long 

 spines. In the inner whorls the ribs are straight, but in the last 

 volution they are slightly flexuous. In the specimen previousl}' referred 

 to as being about an inch in diameter, the sculpture of the early whorls 

 is well exhibited, xlt the commencement of the outer volution of this 

 individual, each rib bears four tubercles, but when it is completed there 

 are eight to each rib ; the process of a gradual division of each tubercle 

 into two separate ones being very clearly shown. At this stage of 

 growth the tubercles are prominent, acute, and are sepai*ated into two 

 sets by a shallowly-grooved space on the periphery. In the penulti- 

 mate whorl the number ot tubercles on each rib is generally twelve, or 

 six on each side, and there are never nu)re than these. They are 

 usually situated at unequal distances from each other, and are sepai-ated 

 by a flattened but not grooved space on the periphery. 



It is only just to the artist to say that the spinous nature of some of 

 the tubercles w^as discovered after the jilates which contain figures of 

 this species were printed. While attempting (subsequently) to remove 

 the matrix from a broken example, a fortunate blow of the hammer 

 exposed three long spines, two of which are very perfect. This specimen, 

 which is represented in the woodcut (fig. 2), is a fragment, consisting of 

 about two-thirds of the penultimate whorl, and a portion of the preceding 



