Reviews—Dr. G. Holm—Hyolithes and Conularia. 369 
points out that they are not in any way related to each other, so far 
as can be judged by the character of the shell; for whilst in the 
Hyolithide this is tolerably thick, not flexible, of at least three 
distinct layers, and mainly of carbonate of lime; in the Conulariidee 
it is thin, apparently flexible, and mainly composed of phosphate of 
lime and chitinous material. Whilst in Hyolithus the shell is bi- 
laterally symmetrical with a differentiated dorsal and ventral surface, 
in Conularia the shell is pyramidal, with a square or rhombic section, 
and with each side marked by a longitudinal median line known as 
the segmental line. A further difference is shown in the fact that 
Hyolithus is provided with an operculum and the aperture is not 
contracted, whilst in Conularia there is no operculum, and the upper 
portion or mouth of the shell seems to have been furnished with 
inwardly bending flanges. 
Besides these two well-marked families, Dr. Holm proposes 
another—Torellide, based on Hyolithus loevigatus, Linnars., the shell 
of which is of phosphate of lime and thus resembles Conularia ; but 
unlike this genus, it is elliptical in section, both sides of the shell 
are alike, and it is without other ornament than lines of growth. 
This form probably belongs to the Annelida, and the author also 
places in the same group the genera Tentaculites and Salterella. 
In the family Hyolithide, the author only recognizes the single 
genus Hyolithus, Hichwald; but this may be divided into Hyolithsu, 
sens. str. and Orthotheca, Novak. This latter sub-genus includes the 
simpler original forms of conical shells with no other markings but 
lines of growth, in which the aperture is in a single plane and the 
‘operculum is a plane, or gently conical and without a semi-conical 
dorsal portion. In the higher developed Hyolithus, sens. str., the 
dorsal margin of the aperture has a semicircular extension, so that 
the aperture is formed by two planes meeting at an obtuse angle, 
and the operculum to fit this aperture, consists of a small lunate 
ventral portion and a larger semi-conical dorsal portion. 
Of the other genera hitherto included in this family, Camerotheca, 
Matthew, Diplotheca, Matt. and Pharetrella, Hall, are brought within 
the type genus, whilst others, as Coleoprion, Sandb., Coleolus, Hall, 
Clathrocelia, Hall, Hemiceras, Hichw. and Hyolithellus, Bill., are 
rejected as having no relationship with it; this latter genus is stated 
to be based on the brachiopod shell, Discinella. Cleidotheca, Salt., is 
founded on the assumption that some of the forms were destitute of 
an operculum, and Centrotheca, Salt., on a probable misinterpretation 
of the characters of the type form, C. cuspidata, Salt. 
Through Dr. Holm’s investigations the number of species of 
Hyolithus from the Swedish Cambrian, Ordovician (or Lower 
Silurian), and Silurian strata has been increased from 6 to 44; the 
greater portion of these are from Oland. From the Lower Cambrian 
or Olenellus region 7 species are recognized; from the Middle Cam- 
brian or Paradowides beds, 15 species; whilst they are scarcely at 
all present in the Olenus division. In the Ordovician or Lower 
Silurian, the Endoceras vaginatum region proved the richest, yielding 
11 species all limited to it, whilst there are several related species in 
DECADE III.—VOL X.—NO. VIII. 24 
