BRACHIOPODA. 13 



passed closely about their insertion, a feature which requires confirmatory 

 evidence. 



In so far, then, as the impressions upon the shell, left by the soft parts of the 

 animal are concerned, we find a close correspondence in the existing and palae- 

 ozoic members of this genus. 



We turn now to a consideration of the septal markings on tlie interior of these 

 shells. When the soft parts are entirely removed from the shell of L. anatina, 

 the pedicle-valve shows a broad, low, longitudinal ridge, whose margins are 

 sharply incised along the posterior portion, but become elevated with the ele- 

 vation of the entire ridge anteriorly. This ridge terminates in front of the 

 center of the shell, and bears, at its excavate extremity, the impressions of the 

 middle-lateral muscles, being buttressed on either side behind these, by the large 

 scars of the centrals. From the posterior extension of this ridge diverge two 

 more or less distinct longitudinal callosities, which are the inner boundaries of 

 the transmedian impressions, or the raised margins of the parietal scars. In 

 the opposite, or brachial valve, a longitudinal ridge is more or less developed 

 toward the posterior portion of the shell, but becomes flattened over the 

 central visceral region, whence it is produced much further forward tlian in the 

 opposite valve, and is sharply elevated. Its terminal portion separates the ante- 

 rior lateral scars, directly behind them lying the central muscular impressions. 

 With these features in mind, we must expect to find the true palaaozoic Lingulas 

 showing evidence, to a certain degree at least, of such internal ridges and cal- 

 losities. In regard to these shell-ridges, King has said : " The muscles, including 

 the parietals, produce scars, often well seen in the valves of recent Lingulas. 

 The scars are occasionally liable to become raised at their margin, giving them 

 the appearance of individualized muscular fulcra or myophores. A specimen 

 before us has the scar of one of the post-lateral parietals with its inner 

 margin completely raised in the form of a plate. Such cases are evidently 

 of abnormal formation ; but they explain the origin of what may be assumed 

 as normal cases — for example, Lingula albida, in which there are two of the 

 same kind of plates "* 



* On Some Characters of Ling-ula anatina. p. 8. 



