108 
THE GEOLOGIST. 
— regards these as being due to the ocdusor (his "valvular") muscles; 
for it is highly probable that these smaller scars in advauce of the 
larger ones were produced by a portion of the occlusors themselves.* 
Immediately imder, but outside of, these thei-e exists two deep, 
longitudinally striated, subquadrate impressions, which are in all 
probability due to divaricator (= cardinal) muscles, but which 
have been referred by Professor King to pedicle muscles, f In vain 
hitherto have I sought for impressions referable to adjustor muscles ; 
but, as no peduncle existed in the Produdidce, such muscle might be 
supposed not to have existed ; however, as the valves of some of these 
forms possess no teeth nor sockets, and, therefore, are not strongly 
articulated, as in the Terehratulidop, it is not impossible that the 
adjusters may have been so arranged in Producta and Aidosteges as to 
keep the valves adjusted to each other, and that they have thus acted 
as a substitute for a hinge, somewhat in the manner Mr. Hancock 
has supposed to be the case in Lingula.\ 
* Mr. Hancock informs me tliat the occlusors are undoubtedly formed of two 
elements, the anterior and posterior, and that we should not therefore be sur- 
}irised to find indications of the two component parts in the ventral as well as in 
the dorsal valve. In Linr/ula the anterior and posterior occlusors are distinct, 
having four points of attachment in eacli valve. 
+ Prof. King has figured in his monograph of Englisli Permian Fossils (PI. XIX. 
fig. 2) what he terms vascular markings in connexion with these large muscular 
scars, and which seem to form part of the impression. Mr. Hancock appears dis- 
posed to consider the whole to be the scar of one muscle, and that there is nothing 
extraordinary in this, as it frequently happens that tlie same thuig may be seen 
in the Unionidce and other Conchifera. 
t Although tlie case in question may not apply directly to Producta, it will be 
as well to mention that Mr. Hancock has found in Linr/ula three pairs of adjusters, 
apparently for the pui-jiose of keeping the valves opposed to each other and of 
holding them adjusted. In this respect, they appear well calculated to compensate 
for the entire absence of hinge or teeth. He explains this in the following words : 
— " The external or ventral pair having their anterior extremities attached to the 
ventral valve — which, as it is fixed to the peduncle, is that from wliich all muscles 
act— and their posterior ends to the dorsal, it is evident that they will prevent 
the latter from being forced backwards ; while the posterior adjusters having their 
terminations united to the ventral or fixed valve, and their anterior portion to the 
dorsal, they wiU act in the contraiy direction, and guard against the pressure for- 
ward ; they will also at the same time prevent any lateral displacement of the 
valves, as their diagonal position will enable them to act transversely, as well as 
longitudinally. The external and central adjusters will, on account of their 
oblique arrangement, exert a similar double influence in front." See Mr. 
Hancock's admirable memoir on the anatomy of the Brachiopoda, published in 
the " Transactions of the Royal Society " for 1858. 
Mr. Howse remarks, in his paper, published in the Annals of Natural History 
(18-57), that, when the cardinal process of Producta is in situ, it fills nearly the 
whole of the umbonal cavity of the ventral valve, and may thus assist in keeping 
the valves in position. It is possihle, however, that futiue researches by the aid 
of better preserved specimens, may enable us to discover some traces of adjustor 
muscles. 
