343 



Discopora^ Lamarck. 

 Escharoides Smitt, part., Umbonula Hincks, 

 Mucronella Hincks, part., RamphostomellaM'. Lorenz. 

 (PL XIX, flgs. 2 a-b, fig. 19 a). 



Two to four spines occur very rarely. The primarj' aperture always lacks 

 hinge-teeth, but is often provided with a fairly narrow, median tooth. The oper- 

 culum is membranous and not separated from the compensation-sac. Symmetric- 

 ally placed avicularia very seldom occur; but a larger or smaller part of the 

 aperture is as a rule on its proximal margin occupied by a larger or smaller, 

 usually strongly projecting avicularium, which may be lateral or median, but 

 frequently has an asymmetrical position. The ocecia, which have a small basal 

 mark, consist of two calcified layers, of which the ectoooecium is provided as a 

 rule with pores. The distal half of each lateral wall is provided with 1—2 multi- 

 porous rosette-plates. 



To this genus belong of the northern species: ^Escharoides" Sarsi, ^Umbonula<^ 

 verrucosa, ^Mucronella* pavonella (which Harmer has already referred to the 

 genus Umbonula), as also the species of the genus Ramphostomella, v. Lorenz. To 

 the latter genus v. Lorenz^ refers 6 species, but the material investigated by 

 me seems to show, that R. costata v. Lor. is not sufficiently distinct from R. 

 scabra. To these has to be added R. ovata Smitt. The genus Discopora stands near 

 to Smittina, from which it differs by the lack of hinge-teeth, by never possessing 

 a symmetrical sinus, by always having some few multiporous rosette-plates, as 

 also generally in the position of the avicularium. The limits between the two 

 genera are however not so clearly marked but that we could imagine them dis- 

 appearing on investigating a larger material. 



The primary aperture, which may be more or less regularly circular or semi- 

 circular, has sometimes a concave, sometimes straight or somewhat convex proxi- 

 mal margin, and in the first case it may be provided with a more or less dis- 

 tinct, narrower or broader sinus (D. Sarsi, D. spinigera, D. bilaminata). Whilst 

 the hinge-teeth are always lacking, a very inconstant median tooth may however 

 appear in most species (lacking in D. Sarsi and D. verrucosa), and there are also 

 in several species one, two or several, conical or trapeziform teeth, as a rule ex- 

 tremely small on the proximal margin of the aperture. Thus, such a tooth oc- 

 curs as a rule on the one or both sides of the above-mentioned, asymmetrical 

 sinus, and in D. Sarsi the number of these small teeth may sometimes mount 



' 84, p. 112. ^ 58, p. 93. 



