DAVIDSON— SCOTTISH CARBONIFEROUS BRACHIOPODA. 227 



Cat Craig, near Dunbar. It occui's also in Edinburgsliire, and along the Ber- 

 wickshire coast, from the mouth of the Tweed to Ross. 



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 

 broader at the front than at the beaks, which are likewise more or less pomted, 

 while the front is either 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 somev/hat more elongated and pointed than that of the ventral one.* 

 The external surface is also either nearly smooth, or concentrically striated. 

 The valves are usually moderately convex, and generally deepest or most 

 elevated 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 slightly 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 togetlier one or other extremity ; nor 

 does there 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 havmg been 

 found at low-water buried in sand. 



The intimate shell-structure of Lingvda 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 thin laminae, which 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, recalling those of the Terebratulidse.f Mr. S. Cloez has like- 



* Anatomists appear to differ as to the names by wMcli the valves should be designated ; it 

 may therefore be as weU to mention those that are synonyms. The shortest is the dorsal 

 valve of Woodward, Hancock, etc. ; = valve inferieure, Gratiolet ; = valve droite, Vogt. 

 The longest is the ventral valve of Woodward, Hancock, etc. ; = valve superiem% Gratiolet ; 

 = valve gauche, Vogt. Mr. Hancock is of opinion that if the names of the valves were to be 

 changed, that they should be caUed 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 palge- 

 ontologists, and have been taken from the first portion of Dr. Gratiolet's recently pubhshed 

 memoir on the anatomy of Lingula anatina ; and I avail myself of the present opportunity to 

 express my grateful thanks to the distinguished French anatomist for the high honour he has 

 conferred by 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, " Me- 

 moire sur TAxiimal de la Lingula :" 1797 and 1802. Vogt, " Aaiatomie der Lingula anatina :" 

 1845. Owen, "On the Anatomy of the Brachiopoda;" "Transactions of the Zoological 

 Society:" 1835. As weU as in. Davidson's "General Introduction," chap. i. : 1853. S.P.Wood- 

 ward's "Manual of the MoUusca: 1854. But especially to the magnificent memoir by Han- 

 cock, "On the Organization of the Brachiopoda," Trans. Royal Soc. : 1858. As well as to 

 Gratiolet's most important and excellent memoir, "Etudes Anatomiques sur la Lingula 

 anatina," in the " Journal de Conchyliogie" for January and April, 1860. 



