16 On some Characters of Lingula anatina. 



Aniferous. 



Splanclmocoele large, and lying within the pallial margins. 



Setal band passing continuously round the pallial margins. 



Genitalia principally enclosed within the splanclmocoele. 



Muscular peculiarities. 



Pedicle not serving as a base of attachment for any 

 muscles *. 



Judging from what Semper and Morse have already made 

 known respecting Lingula anatina and L. pyramidata, it seems 

 highly probable that the section is also distinguished to some 

 extent by its respiratory apparatus. 



The Tretenterates appear to admit of being grouped under 

 two divisions, respectively represented by Lingula and Discina, 

 as the latter genus is strikingly differentiated by its muscular 

 system, pedicle-characters, pallial vessels, and setal band. 



EXPLANATION OF PLATE II. 



All the figures are diagrammatic, particularly figs. 3 & 5. 



Fig. 1. Ventral or pedicle-valve. Splanclmocoele : this chamber in both 

 valves is bounded by the parietal band, b, which I have made 

 to consist of four portions — posterior (behind the part marked//), 

 post -laterals (at the incurvations), ante-laterals (at the ecurva- 

 tions), anterior (extensions in front): c, liver; d, genitalia; 

 e, intestine ; f, termination of intestine ; g, umbonal muscle ; 

 h, central muscles; i, transmedian muscles; lateral muscles (j, an- 

 teriors ; k, middles ; /, outsiders) : m, pleurocoeles ; n, vessels of 

 pleurocoeles (exaggerated) : brachiocoele — all the anterior half of 

 the valves outside the anterior parietal ; p, primary vessels of 

 brachiocoele; q, secondary vessels of brachiocoele (those passing 

 from the inner side of the primaries may be called in-goers, and 

 those on the outer side out-goers) ; u, setal band (the pedicle is 

 not represented, in order to show the continuation of this band 

 in the rostral region) ; v, inner edge of setal band — answering 

 also to the line of vascular constriction ; to, outer edge of setal 

 band; x, seta?. 



Fig. 2. Dorsal valve, r, arms or brachial appendages (relative position 

 and direction of spirals merely shown) ; s, medio-longitudinnj 

 shell-plate ; t, gastro-parietal bands (attached to slightly raised 

 shell- ridges in the valve, and which are represented under t). All 

 the other parts are lettered as in fig. 1. 



Fig. 3. Medio-longitudinal section of cardinal region of both valves. 

 A, dorsal valve ; B, ventral or pedicle-valve : a, deltidium ; 

 d, cardinal or hinge-slope : g, corneous 'or external layer of 

 pedicle — the lower division (or, rather, under face of the pedicle) 

 is attached to a and d' ; h, muscular or inner layer of pedicle ; 

 i, central hollow of pedicle : b, posterior parietal of splanchnoccele ; 

 g, umbonal muscle ; u, setal band ; x, setae. 



Fig. 4. Cardinal region of pedicle-valve, y, pedicle (its attached end is 

 covered by the setal band, u) ; b, posterior parietal (a horizontal 



* In Discina, contrary to what has been stated, the pedicle, which is 

 an external organ, has no proper muscular connexion with the interior of 

 the shell ; the connexion is chiefly vascular and neural. 



