1861.] M. O. A. L. MORCn's REVIEW OF THE VERMETID^. 153 



it is the second in order. The genus Stoa is characterized thus : 

 " Tube testace contourne en spirale orbiculaire et irreguliere d'un 

 forme discoide, renfle et convexe ; dernier tour de'tache du premier, 

 et se prolongeant parfois en un tube droit, ouverture ovalaire, ter- 

 mine' par un opercule solide, calcaire, couique et surcharge, forme 

 par de tres petites bandes circulaires presque subspirales." A conical 

 operculum, which is solid and calcareous, seems so unnatural and 

 without analogy among the Mollusca and Annelida that I suppose a 

 covering of Nullijoora or some other calcareous matter, which I fre- 

 quently have observed, has given rise to the above statement. In 

 the figure of M. de Serres the last whorl of the operculum terminates 

 abruptly at the edge, just Hke the lid of Siliquarius, represented at 

 p. 321 in Chenu's 'Manuel,' which I have never seen so strongly ex- 

 pressed, neither have I seen an operculum of the high conical shape 

 figured. The concavity of the operculum is very different, accord- 

 ing to the species. In the centre of the under side there is often a 

 conical wart, sometimes very prominent ; but I do not believe it is 

 of generic value, as in a series of species it decreases more and more, 

 and finishes by disappearing entirely. In all the smaller species 

 the operculum is yellow with a red central spot, which, as well as 

 the central wart below, is wanting in the larger species. The whorls 

 are generally few and indistinct ; S. megamastus, Morch, has two or 

 three concentric erect laminse, which give the operculum the appear- 

 ance of being threefold. The surface is covered with some exceedingly 

 small bodies — scarcely to be seen with the naked eye — of a cylindri- 

 cal nodulous form, invested with numerous spicula of a glass-like 

 appearance (PI. XXV. fig. 13). These bodies would be of great im- 

 portance for the distinction of species if their form were not altered 

 by exsiccation, and if they were not, on account of their minuteness, 

 exceedingly difficult to be shown in the same position for comparison. 

 They are at once to be distinguished from the bristles of Stephopoma 

 by their microscopic size and, as it seems, the silicious nature of 

 the spicula, which are always broken abruptly like a steel needle ; 

 whilst the spines of Stephopoma are rarely broken. The axis seems 

 to be of the same substance in both genera. The animal is described 

 by Quoy and Gaimard, and Dr. Gray in the ' Spicilegia.' The pro- 

 podium is semilunar with projecting corners, with two rather small 

 approximating pedal tentacula, which appear to be rudimentary or 

 wanting in S. tonganum and S. reticulatiim, Q. & G., whilst they are 

 rather large in S. nebulosum, Dillw., and considerably exceeding the 

 tentacula in size in S. jilatypus, Morch ; a dried specimen of the latter 

 species showed a flat leaf-like propodium, bringing to mind the under 

 lip of the pupa of the Dragon-fly. 



. Sect. a. Dendropoma, Morch. Operculum planiusculum, in- 

 ferne matnmilla centrali validissima, superne laminis 2—3 con- 

 centricis suberectis ; asperitates vertice trijidce, spiculis sulni- 

 latis leviter areuatis. 



5. SiPHONiuM (Dendropoma) megamastum, Morch (PI. XXV. 

 f. 12&13). 



