﻿152 T. Davidson — What is a Brachiopod ? 



mantle ; the two central ones run direct to the front, near to whicli 

 they bifurcate, while the outer ones give off, at intervals, on the side 

 facing the lateral margin of the valves, a series of branches which 

 bifurcate several times, as may be seen in the figures here reproduced 

 from Hancock's admirable work (PI. YIIL Fig. 9, PL X. Fig. 4). 

 That eminent zoologist observes that the inner lamina of the mantle, 

 and more particularly that portion of it forming the floor of the great 

 pallial sinuses, undoubtedly assist in purifying the blood. 



In 1854, in his review of my Monograph on British Fossil 

 Brachiopoda, Oscar Schmidt called attention to an important 

 anatomical omission, namely, the existence of a vast number of 

 microscopic flattened, calcareous, denticulated plates or spiculse on 

 certain parts of the surface of the mantle, which serve, no doubt, 

 to stiffen the portions that contain them. It was, moreover 

 remarked by Hancock, and afterwards by Deslongchamps, that 

 these calcareous plates "are not spread over the entire surface of 

 the mantle, but only over the large vascular sinuses, the arms, 

 and the perivisceral cavity." These spiculse do not, however, ap- 

 pear to be present in every species, being totally absent in 

 Lingula, BJiynchonella, etc. ; but Deslongchamps again observes 

 that, " after an examination of the genera Kraussina, Terehratiila, 

 Terebratulina, Megerlia and Morrisia {Platidia), we find a series in 

 which the number and consistenc}'' of the calcareous portions increase 

 in a very rapid manner, the spicules forming several layers, leading 

 the observer by a series of gradations to the genus Thecidium, in 

 which the spicules are soldered together, occupying the whole of the 

 mantle, and incrusting it to such an extent that the mantle is no 

 longer distinguishable from the shell itself. The mantle forms that 

 calcareous mass, which equals in consistency the brachial append- 

 ages, a fact of which paleeontologists have often, and in vain, sought 

 the explanation." 



The Brachial or Labial Appendages are a pair of singular organs 

 eminently characteristic of the Brachiopoda. They are often, more 

 correctly, termed labial appendages on account of each member being 

 a prolongation of the lateral portion of the lips or margin of the 

 mouth. The lamellibranchs, or conchifera, have analogous append- 

 ages, but very much less developed. They assume different shapes 

 in different genera, and are supported, or otherwise, by the more or 

 less complicated calcified skeleton already described. The brachial 

 or labial appendages, whether they form a pair of long, bent, or 

 spirally convoluted organs, occupy the larger portion of the cavity 

 of the shell, in front of the visceral chamber ; they therefore are 

 mainly composed of a membranous tube fringed on one side with 

 long flexible cirri (PI. IX. Figs. 4, 5, 6), which were not capable of 

 being protruded in those families and genera in which they were folded 

 back upon themselves, and supported by a calcareous skeleton. In 

 Bhynchonella, where the elongated spiral arms are only slightly sup- 

 ported at their origin by two short projecting calcareous processes, 

 they could be unrolled at the will of the animal and protruded to 

 some distance beyond the margins of the valves. "When forcibly 



