324 Proceedings of the Royal Irish Academy. 



as sucli, inasmucli as lie regarded the inner layer of the valves on 

 which the characteristic costse are situated as an annulns or dia- 

 phragm of the same structure as that which we find in the Striatellese : 

 also he considered the costte to be canaliculi, which does not corres- 

 pond with the actual facts of the case. Grunow has the merit of 

 having been the first to point out the error of the opinion of Smith 

 above referred to." — De Danske Diat., p. 92. "Whether the plate bear- 

 ing the loculi is more intimately associated with the connecting- 

 membrane, as Smith thought, or with the valve itself, as Grrunow and 

 Heiberg are of opinion it is, this is certain, so far as my observation 

 extends, that, as Grunow remarks, the plate seems to attach itself more 

 frequently to the valve than to the connecting membrane ; but as the- 

 valves frequently occur without the plate, and the plate is often 

 found detached, I am disposed to consider it not so much an inner 

 layer of the silicious epiderm as a separate formation, and much more 

 intimately related to the diaphragms of the Striatelleae than to the 

 inner layer which bears the costge in the Epithemiae. Smith describes, 

 the loculi as opening by foramina along the line of suture, a statement 

 which Ralfs repeats. I have however failed to notice any such open- 

 ings, the plate having ever appeared to be perfectly solid. Inasmucli 

 as Thwaites considered the occurrence of the frustules in gelatinous 

 cushions the distinctive character of the genus Mastogloia, and other 

 distinguished writers have entertained the same opinion, Grunow's 

 remark on the subject is deserving of attention : " Whether the species 

 of the genus Mastogloia occur invariably in a gelatinous investment, is 

 a matter concerning which I am very doubtful, as in a fresh collection 

 I observed Mastogloia Smithii free, while I found no specimens in a 

 gelatinous cushion" — Yerhand. der K. K. Zool. Bot. Gesel., Band x., 

 1860, p. 575. However this may be, the occurrence of the plate with 

 loculi in the perfect frustule is a mark of distinction which identifies 

 the genus. Further, it was considered by Grunow, that the occurrence 

 of the inner layer with its costate striation, so different from the 

 sculpture of the valve, constitutes a strong bond of afiinity between 

 Mastogloia and Cocconeis. If, however, the opinion I have expressed as- 

 to the distinctness of the plate from the valve be correct, this resem- 

 blance fails, and in the general details of structure the two genera are 

 widely distinct. The process of reproduction in this genus has been 

 observed by Liiders : according to his observations, two mother cells 

 produce two auxospores. Pfitzer, Untersuchungen iiber Bau und 

 Entwicklung der Bacillariaceen, p. 74, remarks, "that in this 

 feature the genus corresponds with the Naviculeas, and not with the 

 Cocconeideffi in which Grunow placed it ; for the latter, out of two- 

 mother cells, develop but a single auxospore." 



Mastogloia lanceolata, (Thwaites.) Marine or brackish water. 



Yalves lanceolate ; marginal plate wide at middle, and gradually 

 tapering to the ends ; loculi narrow, and numerous ; median line 

 slightly undulate ; strongly marked at the central nodule, and greatly 



