Shell-structure in the Genus Lingula. By F. Chapman. 2!> 



Lingula was examined, but, judging from the present study, it was 

 probably a species closely related in structure to L. albida* He 

 did not differentiate the horny from the calcareous layers, although 

 the two structures are presumably apparent in all species of the 

 genus. 



Gratiolet' s Description of Lingula Shell-structure. — In his ex- 

 haustive and classical paper on Lingula anatina^ Gratiolet states % 

 that the shell is composed of alternate layers of corneous or horny, 

 and shelly or calcareous lamina?, the thickness of each varying in 

 the different parts of the shell. He notes that the horny layers 

 prevail towards the external surface, and the shelly layers towards 

 the internal surface. The structure of the horny layers is simple, 

 transparent, and varying from yellow to green in the species 

 examined. Gratiolet further states that he found no traces of the 

 canaliculi in the horny layer, even after the action of caustic 

 potash, and that it is composed entirely of parallel fibres. The 

 shelly layer is described as recalling the shell of the Terebratulida?, 

 being traversed by a multitude of microscopic canals, and covered 

 besides with stria? of extreme fineness. The mean diameter of the 

 canaliculi in the shelly layer in L. anatina as given by Gratiolet 

 is 0-0008 mm. Gratiolet takes exception to Carpenter's statement 

 that the corneous layers in Lingula and Discina (" Orbicula ") 

 predominate over the shelly layers. 



Correlative Evidence in regard to the Observations of the abort' 

 Authors. — A vertical section of the shell of Lingula albida Hinds, 

 from Long Beach, California, taken from the central region of the 

 valve, shows the corneous layers to greatly predominate over the 

 shelly or testaceous layers in thickness ; and this is in accord- 

 ance with the evidence of Dr. Carpenter, who, it is assumed, 

 must have examined a closely-allied, if not the identical species, 

 when he made the above-cpioted observation. In the section 

 before me, the horny layers are from four to eight times the 

 thickness of the shelly layers. The horny layer is, as Carpenter 

 stated, perforated with very fine canaliculi, obliquely set to the 

 lamina?, and closely resembling those of ivory. These canaliculi 

 are much finer than those seen in the same section traversing the 

 shelly layer, which are comparable to the coarser tubules found in 

 the Terebratulidse. In this section of L. albida the tubules of the 

 shelly layer measure 0-00132 mm. in maximum diameter, and the 



* This species is now placed by Dr. Dall in a new genus, Glottidia, in which 

 the pedicle valve hears two diverging parietal ridges, and the brachial valve a 

 median ridge of about the same length. It appears to represent the genus Lingula 

 in American seas. (See Hall and Clarke, Pal. New York, viii. (1892), Pal. Brach. 

 pt. 1. p. 14. 



t Studies anatomiques sur la Lingule anatina (L. anatina Lam.) Journ. de 

 Conch, ser. 2, iv. (I860) pp. 49-172, pis. vi.-ix. 



X Etudies anatomiques sur la Lingule anatina (L. anatina Lam.) -Journ. de 

 Conch, ser. 2, iv. (I860) pp. 59-60. 



