Mr. Robert Garner's Malacological Notes. 363 



tentacles just mentioned are analogous to those surrounding 

 the orifices of the respiratory tubes in bivalves ; and that enig- 

 matical part, the cndostylc, may represent the crystalline style 

 ap[)lied to its use (mechanical support), or at least so much of 

 it as is retained after the loss of the larval appendage. The 

 hirval Ascidian, or the ApjK'ndicularia, constitutes a very in- 

 ditiorent vertebrate — the tail in tiie latter bent forwards at an 

 acute angle to the body or towards the mouth, and its nervous 

 cords (if such they be) seeming scarcely continuous with the 

 cephalic ganglion, and having alternate instead of opposite 

 ganglia, more unlike the vertebrate or articulate type in this 

 respect than are the nerves in the arms of the Sepia or Argo- 

 naut *. 



Bivalves would differ little from the Ascidiaj, provided the 

 test and mantle of the latter were slit ; but in the former the 

 branchiae are more ditFci'cntiated and the circulatory organ 

 move perfect, shelly valves and muscles to close them are 

 superadded — also a foot in most species, developed according 

 to the amount and kind of locomotion required. There is 

 in bivalves no true head ; but the mouth is furnished with lips 

 and two laminated and ciliated palps on each side, distinct 

 from the branchiae but of similar structure, the lips proper 

 sometimes specialized (as in Pecten). 



Amongst bivalves the above remarks only partially apply- 

 to the Brachiopoda, which, if we endeavour to trace their 

 genetic affinities, present us with some difficulties. They 

 have been considered to have the same relationship to, or 

 descent from, the Bryozoa as the Lamellibranchiatc bivalves ; 

 but if so, it must be in a different line, and without the inter- 

 vention of the Ascidia?. It may be questioned what relation 

 the upper and lower valves of Brachiopods bear to the right 

 and left valves of the ordinary Laniellibranchiates. The cross- 

 ing of the principal adductor muscles in the Lingula, and their 

 median union in some Terebratulce^ the compression of the 

 body and arms or tentacles in Brachiopoda generally, in the 

 opposite direction to the arrangement of the body and corre- 

 sjjonding parts in the Lamellibranchiata, the perfect lateral 

 svmmetry in the former, and a tendency to division, seen in 

 Joraminoj notches, or sept<i, in several species (as in T. dijihija)^ 

 whilst there is often a difference, in some respect or other, 



♦ "On the Genus vl/7/x«r//r»/r/rm," by E.I>. Moss,Linu. Trans, vol. xxvii. 

 part 2. See also Us.-<ow'3 Zool.-Embrvol. Investigations (by Dallas), 

 Ann. & Mag. Xat. Hist., Feb. and May 1875. The last writer is defidedly 

 against the molluscous nature of the Ascidia ; and so are others; but the 

 validity of this opinion depends upon the accuracy of minute and difTicult 

 researches upon the nervous ganglion and other parts, and the opposite 

 conclusions of Mr. Hancock are perhaps as reliable. 



