85. 



Ret('lMri(l(te, in a series ol' species of Ihe genus Smitliiiu, in PorclUi coiujiressu and 

 Discopuni Sarsi. A shorter or longer liibe-shapeil peristome willi a pore on tlie 

 frontal wall is found in the genera Adeonclhi, Hasivcllid and Ttihiicellaria, in cer- 

 tain Retepora species (R. cellnlosa, R. Coiichi, R. complanata etc.). in Tessaradonui 

 bovealis, 'Porinao tiibiilosa, Sinittina Lanshorovi, var. persoiiata), whilst a long 

 tube-shaped peristome without pores is found in certain Retepora forms {R. pecli- 

 naUi, R. phoenicea), in certain Cellepora forms (Cellepora tiibulosa, C. bicornis), 

 Lekijthoj)(>r(t hi/strix, TPhijladellai^ geometrica etc. Next, I would point out, as a 

 general result of my investigations on this point, that the peristome in many 

 cases is very inconstant within the genus (e. g. : in the genera Escharella, Sinittina, 

 Discopora, Petralia, Cellepora, etc.), and Hi neks even mentions a series of cases 

 where the peristome in the same sjiecies may sometimes he present, sometimes 

 absent, which for example is the case in '■Lepralia- Pallasiana, Sniiltina trispino.sa 

 and Escharina Diitertrei. Whilst the above-mentioned small peristomial teeth are 

 found constantly in the small genus K.vochella, their appearance is very incon- 

 stant in the genus Escharoides, and on the whole like Waters I cannot attach 

 very great importance to the peristome, which however does not exclude the 

 possibility that ils apperancc may be constant in a series of genera, e. g. in 

 Adeonella, Hasuwllia and Tiibiicellariu. 



The operculum. As all that has been said regarding the systematic impor- 

 tance of the form of the aperture, also holds good as a rule for the form of the 

 operculum, we may here merely take note of the other ditTerences, which a])pear 

 in its structure. As already mentioned, we are able from the difierent relations 

 of the operculum to the frontal cover and the compensation-sac to distinguish 

 between an opercular valve, a simple and a compound operculum. These dille- 

 rences have however only partially a systematic importance. We have a series 

 of examples of the fact that an opercular valve and a sim|)le o[)erculum may 

 appear within the same genus: e. g. in Sleganoporelln and 'I'ludamoporetld, and 

 especially in the last-mentioned we find a series of intermediate forms between 

 the two kinds of operculum. We have other examples in the i)reviously men- 

 tioned species of Caberea and Scruj)ocell(tria, in which the |))esence of a simple 

 operculum seems to be dependent on the strong development of the covering 

 spine. That an opercular valve and a compound operculum can appear in the 

 same genus, we have examples in the genera Adeona, Porella, Escharella, Escha- 

 roides, Snuttina, Holoporella and Chaperia. Whilst for example we as a rule find 

 a compound operculum in Porella and Adeona, there is an opercular valve in 

 Porella la'vis and Adeona violaceu, and while there is generally an opercular 



