SONNINIA CRASSIBULLATA. 353: 
The coiling of the umbilicus may be compared with simplee and substriata as 
under : | 
nuda. simplex. substriata. 
Diameter . a . 190mm. 190mm. 190 mm. 
Umbilicus . : plsaB ros 63). 55 68:13 
Umbilicus one whorl back Sel oe aes DO igs Ode sas 
Umbilicus two whorls back ew eae os WAR Ee 
This rare and interesting species occurs in the Concavum-zone of Bradford 
Abbas. The side view and the outline section of its whorl are shown in figs. 3, 4 
of Pl. LXXXII. 
Sonnrnia orassrpoLiata, S. Buckman. Plate LXXX, figs. 1—3. 
Discoidal, compressed, carinate. Whorls rather flat-sided, in section somewhat 
oblong, ornamented with large, coarse spines passing into bullicoste,' and 
then into direct, upright, subbullate, ventrally-obscure costz. Ventral area 
obtusely arched, divided by a thick, not very elevated, presumably hollow carina. 
Inner margin distinct, broad, nearly upright, flat. Inclusion about three-eighths. 
The bullicostz characterise this species. These coste are intermediate 
between spines and ordinary coste. Where the whorl is not covered they are 
seen to be very different from the spines of the other species because of their 
elongate, obtuse shape.” When the outer part of the whorl is covered they appear 
much like spines ; but they rise from the inner edge at a smaller angle, which is 
maintained until the inner margin of the overlapping whorl is reached. Spines, 
on the other hand, are elevated suddenly, and are carried up sharply alongside 
the inner margin as Jong cones. 
The spinicostz and bullicoste are more distant than would be expected in 
the development of crassiformis ; between nearly each one, also, there is a very 
small plain rib.’ It is therefore hardly possible to derive this species direct from 
adult crassiformis, but it may be linked to the smaller specimen of that species— 
this smaller specimen being regarded as the morphological representative of an 
adult ancestor. Therefore the two series of the crassa-stock may be considered as 
1 Ribs, of which the middle is raised into an obtuse elongate knob. In the inner whorls these 
bullicoste appear rather like spines, but their angle of elevation is less, and is uniform. 
2 Hence the name—dulla =a boss. 
3 In the examples which connect crassibullata and crassicostata an intermediate rib is often 
wanting. 
45 
