344 



up to 4. There is only a single one however as a rule at the subopercular end 

 of the avicularium, but not rarely there is a still smaller one centrally in the 

 sinus. There is also sometimes such a small tooth in D. plicata on the oral 

 margin of the avicularium, but so placed that it cannot be seen from the frontal 

 surface of the zooecium. Whilst a peristome is either quite wanting or weakly 

 developed in those species, which either lack an oral avicularium (D. pavonelld) 

 or in which it has a more or less distinctly median position (D. verrucosa, D. 

 scabrd), it is on the other hand more strongly developed in the other species in 

 which the oral avicularium is lateral. Here, namely, the peristome appears in 

 the form of two projections from the proximal margin of the aperture separated 

 by a triangular incision, and the one of these projections along with an adjacent 

 part of the frontal wall of the zooecium serves as the basal wall of the avicul- 

 arium. What Hincks and v. Lorenz call an avicularium in their diagnoses of 

 the genera Umbormla, Escharoides and Ramphostomella is in reality only the frontal 

 part of the avicularium with the mandible, whilst the avicularian chamber, which 

 contains the muscles, seems to have been either overlooked or regarded as some- 

 thing supporting the avicularium. In Hincks' diagnosis of the genus Escharoides 

 it is said, namely, that the avicularium is enclosed within a sinus, formed by 

 the peristome, while this in reality only applies to the frontal area of the avi- 

 cularium, and in the diagnoses of Umbonula and Ramphostomella the avicularian 

 chamber is described respectively as »a prominent umbo (? avicularian cell) . . . 

 supporting an avicularium* and as » ascending rostra . . . bearing avicularia«. 



The ocecia, which only have a small basal mark, show a similar variation in 

 their structure as in the species of the genus Smittina. As a rule the pores are 

 fairly numerous, though their number may sometimes vary considerably in a 

 single species. Thus, in a colony of D. bilaminata I have found the number of 

 pores varying between 7 and 2. In D. Sarsi there is only 1 or 2, and they are 

 quite wanting in D. ovata which also differs from the other species in that the 

 zooecial wall is provided with scattered pores. An ooecial cover is present in most 

 species and appears as a rule in sufficiently old ocecia as a covering lamina in 

 the marginal region of the ooecium. It is well-developed in D. verrucosa and D. 

 scabra, which resemble one another in most respects and differ chiefly in that 

 the avicularian area in the latter is placed asj^mmetrically. An ooecial cover is 

 most strongly developed in D. Sarsi (PI. XXIV, fig. 2 a) and the ocecia are here 

 rather quickly covered by 3—5 different calcai-eous laminae meeting in a suture, 

 the two proximal of which come from the peristome, the unpaired from the dis- 

 tal zooecium and the remainder from two neighbouring zooecia. 



