Clark — Holophytic Plankton of Lairs Atittan and Amatittan 101 



22. Fragilaria crotonensis Kitton. 



Fragilaria crotonensis Kitton, Science Gossip, 110, fig. 81, 1869; Van 

 Heurck, Treat. Diatom., 324, p. 11, fig. 44, 1896. 



Several examples which I identify with some doubt as this species were 

 found in sample No. 5, collected February 16, at the depth of 120 feet of 

 St. Lucas. They agree fairly well with Van Huerck's figures. 



23. Melosira crenulata (Ehrenberg). 



Gallionella crenulata ~Ehrenberg, Phys. Abh. Akad. Wiss. Berl., 1841; 441, 



pi. 3, fig. 28, and p. 444, pi. 4, fig. 31, 1843. 

 Melosira crenulata Wolle, Diatom. U. S. pi. LVII, fig. 16-20, 1890; Van 



Huerck, Treat. Diatom., 443, pi. 19, fig. 618, 1896. 



One of the most striking features of the Amatitlan plankton is the 

 abundance of Melosira., which is found abundantly in the bottom of nearly 

 all the hauls and usually makes up the main mass of the filamentous mate- 

 rial. Samples of the mud from the bottom of the lake are also full of the 

 f rustules of this species. Although not agreeing in every respect with the 

 descriptions found of M. crenulata it approaches it more nearly than 

 anything else I can find described, and I provisionally identify it as that 

 species. The f rustules are, in some cases at least, broader than long (some 

 measured specimens being 20m in diameter with cells 15^ long) which is 

 not the proportion for crenulata, in which the cells are longer than broad. 

 The specimens occur as long, rigid filaments, exceedingly and surprisingly 

 various in diameter. The chloropasts are in the form of green oval bodies 

 about the middle of the cell, so that the general appearance is strikingly 

 like a confervoid alga, the differences only appearing manifest upon sharp 

 focussing which reveals the characteristic diatom sculpture on the cell 

 walls. The old cell walls project from the end of the filament in the form 

 of long sharp needles, one usually being longer than the other, and there 

 are traces of minute teeth along theends of the filament. As Hassall ( Brit. 

 F. W. Alg., I, 397) aptly remarked, "The genus Melosira amongst the 

 Diatomaceje seems to have been constituted with a view of making appa- 

 rent the affinity between the Diatomace;e and the algse proper" (this was 

 written when the relationship of the diatoms was still a matter of doubt, 

 some contending that they belonged to the animal kingdom). 



Concerning another species (varians) of Melosira, Apstein (Siissw-p., 

 140) makes the following significant remarks, which are also probably 

 applicable in the case of this species : 



"Melosira habe ich direkt als Nahrung von Bosminien, Daphnien und 

 Diaptomus schon 1892 (Biol. Centralblatt Bd. 12, No. 16, 17, 1 Sept., 

 1S92) nachweisen konnen bei denen ich die zellen dieszer Algen deutlich 

 und zahlreich im Darm sehen konnte." 



Order ULOTHRICHACELE. 



24. Hormospora sp.? 



Hormospora forms, consisting usually of 4-8 very short dark green cells, 

 arranged in a short filament and surrounded by quite thick cell walls, were 



