142 



Royal Society : — 



heimia australis, W. Cranium, Terebratulina caput-serpentis, Rhyn- 

 chonella psittacea, Lingula anatina, and another species of Lingula. 



The Brachiopoda are divisible into two groups, according as the 

 valves of their shells are articulated or not. Waldheimia is the type 

 of the former group, Lingula of the latter. 



In the articulated forms there are usually three apertures opening 

 into the pallial chamber ; of these, one is the mouth, — the other two 

 are situated at the apices of the organs which have been described as 

 "hearts." In Rhynchonella, where there are four such "pseudo- 

 hearts," there are of course five apertures instead of three. In Lin- 

 gula, which possesses a distinct anus, opening on the right side of 

 the pallial cavity, the apertures into the cavity are four, viz. one oral, 

 one anal, and two appertaining to the pseudo-hearts. 



After a description of the general arrangement of the organs in the 

 articulated and non-articulated Brachiopoda, an elaborate account of 

 the various systems of organs is given. 



The muscles of the Terebratulidse are divisible according to their 

 functions into two groups, — the adductors of the valves, and those 

 which adjust the shell upon the pedicle. Of the former, or " val- 

 vular " muscles, there are three pairs, — the adductors, cardinals, and 

 accessory cardinals of previous writers ; which the author prefers to 

 term occlusorsy divaricators, and accessory divaricators. Of the latter 

 there are likewise three pairs, the so-called dorsal and ventral pedicle 

 muscles and the capsular muscle ; these the author terms the dorsal 

 and ventral adjustors, and the peduncular muscle. The attachment 

 of the muscles in Waldheimia australis and their actions are par- 

 ticularly described. The peduncular (capsular) muscle is shown to 

 be the continuation of the muscular fibres contained within the pe- 

 duncle. In the other articulated Brachiopoda examined, the arrange- 

 ment of the muscles is essentially the same, but interesting differ- 

 ences are observable even in closely allied species. 



Thus, in a species differing but little from Waldheimia australis, 

 and in W. Cranium, the divaricators and accessory divaricators are 

 united. In Waldheimia Cranium and Terebratulina caput-serpentis 



