1883.] 



MICROSCOPICAL JOURNAL. 



31 



great many frustules and fragments 

 in various conditions, that afford a far 

 better opportunity for the study of the 

 histology, construction, and variations 

 of this order of algte, than many 

 times the number of perfect frustules. 



I have identified the species named 

 below. The comparative abundance 

 of the different forms is indicated as 

 follows: — V. r, very rare, r, rare, c, 

 common, v c, very common. 



Syiiaira c/irystclina, \. r. Cavipcllo- 

 discus echinus, Ehr. C. argus, B- 

 crebosis, W. S., c. Plagiograma staii- 

 roptcra, Grev., r. Tcrpsinoc musica, r., 

 (i). Orf/wsira marina, \. c. Hyalodis- 

 ais subtiiis, B., c, (2). Triceratium 

 firmutn, r. T. Favus, v. c, (3). T. 

 Cottdiconim, c. Navicula didyma, c. 

 N. marina, Ralfs, c. N. pundulata, 

 W. S., r. N. lyra, c, (5). N. per- 

 magna, B., c. IV. interrupta, B., c. 

 N. spiculata, Breb., r. Pkurosigma 

 balticum, r., (4). Adinocydiis, Ehr., 

 with 6, 7, 8, 9, 10, 12 and 16, rays, v. c. 

 Stauroneis aspsra, c. Auliscus priii- 

 nosis, B., v. c, (6). Auliscus ccelatiis, 

 B. et Grev., r. {Trans. Mic. Soc, 1863, 

 //. II, Jig. 5.) Gra?nmatop/iora mncil- 

 lenta, c. Amphipkura longa, Cleve, vel 

 A. Icpidopcra, Greg. ? v. r., (9). Eu- 

 podiscus argus, Ehr., c, (8). E. 

 Rogersii, B., c. E. radiatus, B , v. c, 

 (7). Nitzschia Brightwelli. N. punc- 

 tata, B., V. c. 



1. I have found no example of 

 this perfect enough to positively ident- 

 ify the species. All the species that 

 I have seen figured may be only 

 varities of T. musica. 



2. Much variation in the fineness 

 of the striffi. 



3. This form is very common. It 

 is smaller than usual, but variable, 

 sides slightly convex, and processes at 

 the angles more prominent and con- 

 spicuous than usual. I have met with 

 a few examples of a character that I 

 have before seen on specimens from 

 the Atlantic coast, which appears to 

 have been heretofore unnoticed, viz., 

 there is a marginal row of vertical 

 processes seen in the front view, com- 

 pletely surrounding the triangular 



disc, like a fence. That it is so rarely 

 seen, must be that owing to its extreme 

 fragility it is seldom preserved in the 

 mounting. 



4. This has closer striae than 

 usual. 



5. N. Lyra, very variable, mostly 

 of the apiculate variety. 



6. Auliscus pruinosis, B., A. ccela- 

 tus, B. 



The first of these is very abundant 

 and very variable both in size and 

 markings. 



A. ccBlatus is less common. Gre- 

 ville compares the markings of prui- 

 nosis to scratches on glass with a 

 diamond. The marks on A. ccelatus 

 are smooth, transparent as glass on 

 the best examples. The scratch-like 

 lines of Greville are the most con- 

 spicuous distinction between the two 

 species, for, taking all the variations 

 into consideration it is impossible to 

 draw the line where one species be- 

 gins and the other ends, though the 

 extremes are so distinct. It would 

 be legitimate to reduce Bailey's and 

 Greville's {Tra?is. Mic. Soc. Vol. 

 XI. n. s. pi. 1 1, figs. I to 8, 1 1, 12, 13, 

 18, 19, 20) to one species, for, not- 

 withstanding the difference between 

 figs. I and 22, all have a character in 

 common, the differences being of no 

 specific value, and so variable that it 

 is difficult to find two alike. 



7. Eupodiscus radiatus, B., is the 

 most abundant form. It is very vari- 

 able in size like the last, unlike that 

 the frustules have not been affected 

 by decomposition, but are as perfect 

 and unchanged as if living yesterday, 

 and from the smallest to the largest, 

 the specific characters, are identical. 



8. EupodicHsa?'gus, Ehr., E. Roger- 

 sii, B. This form is more decom- 

 posed than any of the others, and in 

 consequence its study has yielded 

 more important results. It is a form 

 that has become familiar to all who 

 have Moller's probe- and typen-platte, 

 and is common in many places. 



Bailey figured Eupodicus Rogersii 

 and gave a figure descriptive of it, 

 which is copied into Pritchard. Both 



