MARINE DIATOMS OF THE PHILIPPINE ISLANDS 89 



This is possibly the same as the unnamed figure in Schmidt's Atlas, 

 plate 187, figure 36, from Cebu. Rare, in only one dredging. 

 Type.— Cat. No. 43635, U.S.N.M. 



MASTOGLOIA GRUENDLERI A. Schmidt 



(Schmidt, Atlas, pi. 188, fig. 26.) 



This is another species found only at Campeche Bay and the 

 Philippines Islands. 



MASTOGLOIA IMITATRIX, new species 



Plate 19, fig. 4 



Valve convex, narrowly oval in outline, slowly tapering to the blunt 

 rounded apices; the rhaphe is strongly oblique, that is to say, it is 

 diagonal to the long axis, but runs straight until near the apices where 

 its two ends curve strongly to opposite sides; adjacent to either side 

 of the rhaphe is a parallel line; the central nodule is slightly 

 dilated but is not surrounded by a hyaline central area; the valve 

 markings are delicate, closely set lines obscurely crossed-marked, 

 reaching the parallel lines bordering the rhaphe, transverse until near 

 the ends and there slightly oblique; the lateral rows of chambers lie 

 next to the rim, are all of the same size, the terminal ones being ta- 

 pered and do not reach the apices; in side (girdle) view there is 

 seen to be a slight depression of the valve across its middle; the ends 

 are bluntly rounded; the girdle is hyaline and is not oblique. 



Length 0.071; width 0.047; 15 lines in 0.01 ram., 3 chambers in 

 0.01 mm. 



The striking imitation by this unmistakable Mastogloia of Scoli- 

 opleura tumida Brebisson raises interesting questions of relationship, 

 especially when taken in connection with the fact that W. Smith 

 called the latter Navicula jenneri and Cleve restores it to that genus 

 under the name N. tumida (Brebisson) Cleve, and also when we re- 

 member that many examples of Mastogloia differ from Navicula only 

 in the presence of the chambered compartments along both sides of 

 the valve. For we are herein led to ask if these internal rows of 

 chambers are anything more than persistent craticular structures, 

 homologous with the craticular plates sometimes observed in certain 

 Naviculae, such as N. cuspidata Kiitzing. N. ambigua Ehrenberg, etc. 

 It was my good (or bad) fortune to disturb the specimen here illus- 

 trated after it had been mounted in face view and its compartments 

 had been studied and measured ; so that it turned over into side (girdle) 

 view and thereby enabled me to see that the lateral rows of chambers 

 occupy their usual position within each valve. It is true this species 

 is different from Scoliopleura tumida, in having more truly transverse 

 and somewhat finer lines of sculpture, in the absence of any hyaline 



