DAVIDSON- 
: — SCOTTISH CARBONIFEROUS BIUCIIIOPODA. 
227- 
Cat Craig, near Dunbar. It occurs also in Ediuburgshirc, and along the Ber- 
wickshii'e coast, from the mouth of the Tweed to lloss. 
Family Lingulid.*:. 
Genus Lingula. Bruguiere. 1789. 
The limit of variation among the shells composing the genus Lingula appears 
to be more restricted than what is prevalent among the generality of other 
genera and species of Brachiopoda. It is, therefore, very often no easy matter 
to distinguish and correctly determine some fossil species, even when occurring 
in different and often widely separate geological periods. 
The shell of Lingula is thin, equilateral, usually longer than wide, and 
l)roadcr at the front tlian at the beaks, whicli are likewise more or less pointed, 
while the front is eitlier nearly straight, or with a slight inward or outward 
curve. The shell is also sub-equivalve : the extremity of the beak of the dorsal 
valve is somewhat more elongated and pointed than that of the ventral one.* 
The external surface is also either nearly smootli, or concentrically striated. 
The valves are usually moderately convex, and generally deepest or most 
ele\'ated towards the beak, and become more flattened as they approach the 
front. The apex of the dorsal valve is likewise situated quite close to, but not 
contiguous with, the rounded margin of the beak, and by which character the 
valves can be readily distinguished, both in the recent and fossil condition. 
When alive, the valves of Lingula were sKghtly gaping at each end, con- 
tiguous only along the lateral margins ; but the animal could at its will, by the 
action of certain muscles, close or draw together one or other extremity ; nor 
does tliere exist any articulation, the valves being kept in place by the means 
of a complicated system of muscles, to be hereafter described. The animal was 
also provided with a very long pedicle of a peculiar construction, which was 
chiefly attached to the inner groove, situated in the beak of the ventral valve ; 
and when alive did not inhabit great depths, most recent species having been 
found at low-water buried in sand. 
The intimate sheU-structure of Lingula has been described by Dr. Carpenter; 
and we will therefore only refer to Dr. Gratiolet's and Mr. S. Cloez' more recent 
observations. The first named savant states that the shell is composed of two 
distinct elements, the one being horny, the other shelly ; that they are disposed 
in layers, or tliin laminse, whicli succeed each other alternately from the con- 
vex surface of the valves, the outer or superficial one being horny ; that these 
layers have not the same thickness, the testaceous ones being thickest on and 
near the visceral side, while the horny ones are more so towards the exterior 
surface ; and that while the horny layers are entirely formed of parallel fibres, 
without trace of perforations, the testaceous ones are traversed by a multitude 
of minute canals, recaUing tliose of the Terebratulidee.f Mr. S. Cloez has Hke- 
• Anatomists appear to differ as to the names by which the valves should be designated ; it 
may therefore be as well to mention those that are synonyms. The shortest is the dorsal 
valve of Woodward, Hancock, etc. ; = valve inf(5rieure, Gratiolet ; = valve droite, Yogt. 
The longest is the ventral valve of Woodward, Hancock, etc. ; = valve superieiir, Gratiolet; 
= valve gauche, Vogt. Mr. Hancock is of opmion that if the names of the valves were to be 
clianged," that they should be called anterior and posterior. In the present paper we will 
continue to make use of those first mentioned. 
t I have considered it desirable to reproduce these details, as they are new to British pale- 
ontologists, and have been taken &-om the first portion of Dr. Gratiolet's recently published 
memoir on the anatomy of Linijula aiuitiim ; and I avail myself of the present opportunity to 
express my grateful thanks to the distinguished French anatomist for the high honour he has 
confei'red liy dedicating to me the results of his admirable researches. For details concern- 
ing the animal of Lingula, I must refer the reader to the following memoirs : — Cuvier, " M^- 
moire sur rAnimal de la Lingula :" 1797 and 1802. Vogt, " Anatoraie der Lingula anatina :" 
1845. Owen, "On the Anatomy of the Brachiopoda;" "Transactions of the Zoological 
Society:" 1835. As well as in Da\'idson's "General Introduction," chap. i. : 1853. S.P.Wood- 
ward's "Manual of the MoUusca: 185-1. But especially to the magnificent memoir by Han- 
cock, "On the Organization of the BrachioiJoda," Trans. Royal Soc. : 1858. As well as to 
Gratiolet's most important and excellent memoii', "Etudes Anatomiquea sur la Lingula 
anatina," in the " Journal de Conchj-liogie" for January and April, ISfjO. 
