LIVING BRACHIOPODA. 321 



SHELL. 



The word shell is hardly appropriate except as a common term for all hard coverings, 

 such as nut-shell, egg-shell, bomb-shell, and the like. The shell of the Brachiopoda in 

 composition, structure, and relation to the soft parts has no relation whatever to the 

 shell of the Acephala. The words scale, scutum, and elytron are equally used in widely 

 different groups. For convenience of designation, however, the word shell will be used in 

 reference to the outer hard parts of the Brachiopoda. It is desirable, however, that 

 appropriate names should be given to the hardened integument of the different groups 

 of animals supporting such coverings. 



Unless the shell of Lingula be drawn from life, or from well preserved alcoholic 

 specimens, it is, with some exceptions, impossible to get an outline of any specific value. 

 These exceptions are the larger and heavier shells, such as those of Lingula anatina, 

 wherein a heavy deposit of limy matter renders the shell more rigid, though even here a 

 region of the shell extending in a median line from the peduncular end is generally 

 represented a little more arched than in nature. In the diaphanous forms, such as 

 Glottidia and the smaller species of Lingulae, the shells warp and twist quite out of shape. 

 In one case the anterior half of the shell turned upward until the lateral edges touched 

 in a median line. Outlines of the shell of Lingula lepidula drawn from life are presented 

 at 42 : 5, while 42 : 6 represents the same shells removed from the body and allowed to 

 dry slowly. A line below each set of figures shows the outline of the dorsal shell across 

 the back transversely. The rounded ridge or cariuation, represented in the figures as 

 running from the posterior end of the shell forward, has no existence in nature. In view 

 of these facts it is no wonder that there is much confusion regarding the smaller and 

 more diaphanous species of Lingula. 



While the shells of Linyulidae collected at any one time vary but little in size, by 

 comparing a number of specimens a series of broad and of narrow forms may be observed. 

 These variations were so marked in L. lepidida that I thought the differences might be 

 sexual. A further comparison showed that these variations blended and so the broad and 

 narrow forms may be regarded as the extremes of variation. The extent of this variation 

 is shown in 42:5. These differences were noted in L. anatina, L. lepidula, and G. 

 pyramidata. 



I have designated under setae, the long clusters of setae near the hinder third of the 

 body, as the posterior cluster. The variation in the width of the shell is marked by a 

 broadening of this region. In L. anatina the anterior margin is in some specimens 

 pointed or beaked in the median line, in others it forms a rounded or flattened curve. 



