72 0. M. DAWSON OS A NEW SPECIES OF 



spocios, " primarily of a continuous lamina coilod upon itself, like a 

 scroll coustrictcd at the ends. The space enclosed by this ' primary 

 lamina ' is divided into chambers by longiludinal septa. The septa 

 are of ' secondary ' growth ; that is to say, they are not continuous 

 with the principal wall or ' spiral lamina,' but are rather otfshoots 

 from it"*. As seen in a transverse section of the test, these septa 

 are not perpendicular to the spiral lamina, but very oblique to it ; and 

 on further examination they are found to lie nearly parallel to the 

 surfaces of a supposed second scroll, concentric with the first, but 

 not, like it, constricted at the ends. Tlie lines of intersection of the 

 " secondary " septa and " jjrimary "' lamina make, therefore, curved 

 or oblicjue outlines on the surfaces of the latter. The 8e|)ta sliow, 

 however, as straight or nearly straight lines in longitudinal and tan- 

 gential sections. 



A series of " tertiary " ingrowths further pass between the opposed 

 surfaces of the " i^rimary " lamina and those and the "secondary" 

 septa. These processes are in the form of pillars, and are arranged 

 in rows, longitudinally and transversely, appearing most regidar 

 in a longitudinal section. They are at right angles, or nearly so, 

 to the "primary" lamina. The structure is further complicated by 

 the fact that the " tertiary " columns, where they attach tliemselves 

 to the spiral lamina; at their distal extremities, expand into a more 

 or less regular cross-shaped form, the arms of whicli, uniting with 

 those from the neighbouring pillars, form a reticulated framework. 

 This, owing to the regularity of position of the columns, may almost 

 be considered as forming a system of crossed rafters supporting the 

 " roof " of the space contained between each two consecutive folds of 

 the " primary ' " lamina, while the columns do not show any such ex- 

 pansion on the " floor." The spaces between the expansions or 

 rafters, constituting a series of imperfect chambers, are further tilled 

 with a loose cancellated growth, which sometimes depends more than 

 halfway to the " floor." This represents the system of " irregular 

 anastomosing tubes " and " parallel columnar or tubular processes " 

 occupying a like position in L. pcrsica ; but in the form now under 

 consideration, probably owing to the greater size of the calcareous 

 particles in proportion to that of the test, and its consequent rougher 

 construction, no distinct tubulation is recognizable. 



The greatest number of convolutions of the " primary " lamina 

 actually observed is seventeen. Ten is a very common number in 

 average-sized specimens. The average breadth of the space enclosed 

 between two successive convolutions of the lamina is one hundredth 

 of an inch ; and this is maintained with considerable regularity, 

 though in young specimens the first two or three whorls are much 

 less. The " tertiary " processes or pillars, and the bars of the reti- 

 culated framework connected with them, are generally in diameter 

 from one four-hundredth t(> one three-hundredth of an iuch, very 

 rarely as much as one hundredth. 



The " primary " lamina, as in L. perslca, is a thin and definite 

 wall, generally appearing in microscopic sections as a well-defined, 



# Op. cif. p. 743. 



