16 On some C/<«mc^e?'s 0/ Lingula anatina. 



Anifcrous. 



Splanclinocoele large, and lying within the pallial margins. 



Setal band })a.ssing eontinuously round the pallial margins. 



Genitalia principally enclosed within the splanchnocoele. 



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 re])resented by Lin<jula 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 figiu-es are diagrammatic, particularly figs. 3 & 5. 



Ftff. 1. Ventral or pedicle-valve. Splanchnocoele : 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 (7), 

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

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

 e, intestine ; /, termination of intestine ; (/, umbonal muscle ; 

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

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

 pleurocoiles (exaggerated) : brachioccele — all the anterior half of 

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

 brachioccele ; q, secondary vessels of brachioccele (those passing 

 from the inner side of the primaries may be called in-r/oers, and 

 those on the outer side out-(/oers) ; ti, 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 ; .r, setfe. 



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

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

 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. L 



Ftff. 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 splanchnocoele ; 

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



Fiff. 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 chieflv vascular and neural. 



