CEPHALOPODA. 
245 
to the depth of the chambers. Specimens in which the 'siphnncle has 
become exposed by weathering, show that it was obscurely lobed and longi¬ 
tudinally ribbed. 
The test was probably thin. No portions of it are preserved in any of 
the specimens observed. The surface, as shown by the internal casts of 
several individuals, was marked by lamellose, transverse striae. 
The appearances of the internal mould of this species are very character¬ 
istic. The exsolute, or lax condition of the chambers, together with their 
concave margins — a uniform condition of the compressed specimens—is a 
distinguishing feature. The organic deposit is shown in all casts of the 
interior, and is peculiar to the species. 
The largest fragment referred to this species has a length of 200 mm. 
Other fragments have been found belonging to larger individuals. The 
maximum length was probably not more than 400 mm. 
The organic deposit on the septa, around the siphuncle, and on the ventral 
walls of the air-chambers, presents many different aspects, and has been 
observed in numerous individuals. It increases in amount and complexity 
of detail, from the chamber of habitation to the apex. In some specimens 
the siphuncle has been absorbed or obliterated by the deposit. Other speci¬ 
mens show a deposit formed on the interior of the siphuncular tube. The 
filling up of the chambers is not, however, carried to such a remarkable 
extent as in 0. opplctum, but is much more marked than in any of the pre¬ 
ceding species. The deposit on the septa varies in different portions of the 
tube, and on different sides. Sometimes the amount is very marked on one 
side (see fig. 3, pi. 78 B), and less prominent or nearly absent on the other. 
The appearance produced is generally a pitting or erosion of the material 
filling the chambers. In well-preserved specimens, it is shown that these 
pits are the casts of the original deposit, which consists of closely arranged, 
irregular, mammillary aggregations of calcareous matter. The globules com¬ 
posing these masses are usually very small, occasionally reaching a diameter 
of two mm. The appearance around the siphuncle is, at first, that of a 
simple areola; the amount of deposit increasing till it becomes thickened, and 
