464 



la the articulated forms there are usually three apertures opening 

 into the pallia! 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 occlusors, 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 adjusters, 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 

 the dorsal adjuster muscles are not attached to a hinge-plate, but are 

 inserted into the valve itself. In Rhynchonella psittacea there is a 

 pair of peduncular muscles. In Lingula there are six pairs of muscles, 

 all of which have both extremities attached to the valves. They have 

 been divided into adductors and sliding muscles, the latter again being 

 subdivided into protractors and retractors ; but the author, con- 

 sidering that no sliding motion takes place, regards the latter terms 

 as improper, and gives a set of new names, of which a concordance 

 with the olderdenomiuations is subjoined. 



