THE BRITISH FOSSIL BRACHIOPODA. 293 



no canals, the shell being found to consist of flattened prisms of considerable length which 

 lie parallel to one another with great regularity, and at a very acute angle to the surface 

 of the valves. This is the case in all the specimens of Fischer's genus Rliynchonella ; but 

 in another closely allied genus, Bhynchopora (King), and notably in the Rhynchopora 

 Geinitziana from the Permian of Gera in Thuringia, Professor King discovered that some 



mediate division (c of woodcut) is a thin calcareous lamina, just appreciable as such in Waldheimia australis 

 and other recent species, lying between the epidermis and the prismatic shell-layer, and distinguished 

 from the last by having a much finer divisional structure ; it being for the most part fibrous and compact 

 in the inner portion, and apparently granulo-fibrous and somewhat loose in Shell-structure. 



texture in the outer portion, that is, immediately subjacent to the epidermis. 

 I detected it first in Productus horridus under the form of a • thin superficial 

 lamina' overlying the prismatic division (a of woodcut), and it has occurred 

 to me in several other fossils, particularly String 'ocephalus Burtini. In some 

 cases it may be a calcified form of the epidermis. The three divisions are so 

 intimately united as to be with difficulty obtained in a separate state. The 



* l a. Prismatic shell-layer. 0. 



epidermis of Megerlea truncata may in some cases be peeled off from the Outer division, c. Intermediate 



subjacent layer, while the latter occasionally occurs dissevered from the of^lrforatitn. ^^SiatiLg 

 prismatic division in broken specimens of the valve of this and other species, closely-packed hairs. 



" The canal-system, so characteristic of many palliobranchiate shells, first became a generally received 

 fact through the researches of Dr. Carpenter, published in 1843 and subsequently; it was to some extent 

 previously known, however, to a few palaeontologists, notably Prof. Morris, in 1 84 1 (see 'Mineral Conchology,' 

 No. 108, p. 12, March, 1841). It consists of perforations or tubes, which are generally described as passing 

 through the valves ' from one surface to the other ;' but, strictly speaking, this is not correct, for their 

 upper portion terminates against or near the under surface of the epidermis. Just before reaching this 

 part the perforations assume a feature not seen elsewhere throughout their length or lower down ; thus on 

 entering the intermediate layer they suddenly become dilated, and their aperture or mouth, which is 

 more or less contracted, according to species, by an inwardly projecting rim, abuts against the under 

 surface of the epidermis (d of woodcut). The lower half of the perforationsis often considerably smaller in 

 diameter than the upper one. The apertural rims, in specimens which retain the epidermis, appear 

 under a common lens like minute oval or circular spots, often quincuncially disposed over the surface of 

 the valves. When examined with a moderate magnifying power the apertural rims are each seen to be 

 densely crowded with short, excessively fine lines radiately intersecting them, or, in other words, the spots 

 resemble brush-like bundles composed of short, closely- packed hairs radiating from a vacant centre (e of 

 woodcut), often of considerable width, as in Megerlea truncata, but much smaller in Terebratulina caput- 

 serpentis and some other species, &c. 



" Crania anomala agrees with the Ancylobranchs in having both valves perpendicularly perforated; 

 but this character is not, as in them, distinctly manifested on the outer surface of the shell. In the upper 

 valve the perforations, somewhat slender, are widest at their base, that is, where they open out on its inner 

 surface ; in other words, their apertures, when observed with a high magnifying power, are seen to be funnel- 

 shaped, and separated from one another by a tolerably well-defined ridge-like space ; but, with a lower 

 power, they simply appear to be separated by a space approximately equal to their own diameter. The 

 apertures occur on the whole of the inner surface of this valve, and they also occur on the corresponding 

 surface of the lower one. Leaving the contracted portion of their funnel-shaped base the perforations 

 pass upwards, with a slight attenuation, towards the opposite surface of the valve ; but generally, on 

 reaching the brown layer, they become divided, each one splitting into three, four, or more widely diverging 

 branches," &c. 



