NATURAL SCIENCES OF PHILADELPHIA. 343 



The rudimental alae, which in the Fig. 3, a, are represented as marginal, oc- 

 casionally assume a submarginal position, and when this occurs in the 

 smaller valves, it would be difficult for any one not familiar with the larger 

 varieties to distinguish them from Amphipleura sygmoidca, to which species the 

 resemblance is very marked. The brackish habitat and much finer striation 

 of this latter diatom, however, make it impossible that they can be identical. 



In Fig. 3, b, the peculiar arrangement of the alae is tolerably well shown, 

 as rendered from the dry valve. These it will be seen are feebly defined, 

 and, owing to their somewhat exceptional (for Surirella) relations to the valvu- 

 lar surface, present an inverted appearance. Viewed from what I believe 

 to be the inner aspect of the valve, they are hardly distinguishable from 

 puncta, and occasionally seem to be obsolete. Owing to the brittleness of 

 the connecting membrane, it is difficult to get a front view of the frustule, 

 excepting in the recent specimen, and the valve is best studied by burning 

 this upon a thin glass cover. 



IV. Surirella delicatissima, n.sp. The next species is exceedingly minute 

 and variable. Frustule straight. F. V. Linear slightly inflated with rounded 

 ends. V. linear lanceolate, sometimes centrally constricted, with produced, 

 rounded, or subacute extremities. Alae marginal, inconspicuous ; canaliculi 

 obsolete ; striation very delicate. 



This very minute form is abundant both in the Saco and Wolfboro' muds ; 

 but being feebly silicious and the valve highly refractive, it is apt to be over- 

 looked in acid-boiled and balsamed specimens. It varies greatly in outline 

 and definition of alae. The Fig. 4, a, b, represents the most usual form. The 

 marginal lace-like border is very elegantly displayed, in the larger frustules 

 burnt on glass. 



This species is specially interesting, as approximating a step nearer the 

 Synedroid type, in the absence of canaliculi, and the attenuated form of 

 the valve. 



It may , perhaps, turn out to be an early stage of*?. Baileyi. The specimen 

 figured is magnified 1000 diameters. 



I now pass on to consider a very curious and anomalous diatom nearly al- 

 lied to Eunotia, and more remotely to Asterionella, but with points of differ- 

 ence from either, so decided as, in my opinion, to require its isolation in a 

 separate genus. This, from the radiant arrangement of the frustules, I pro- 

 pose terming " Actinella," nov. gen. "Frustules linear arcuate, with an une- 

 qually notched inflation at one extremity, and terminal nodules, usually form- 

 ing, by the adherence of the smaller ends, a stellar grouping." 



V. Actinella punctata, n. sp., is the only species yet found. Frustules lin- 

 ear, arcuate, commonly in radiating, symmetrical clusters of from six to 

 twelve individuals. " F. V. straight, slightly cuneate, narrowing gradually 

 from the extremities towards the centre ; ends more or less truncate. V. ar- 

 cuate with a well marked notched inflation at the free extremity, smaller 

 (attached) end rounded, with terminal nodules and sharp convergent striae, and 

 a row of marginal puncta." Habitat on the surface mud. Fig. 5, a, b and c. 



The idea first suggested by the singular irregularity of development in this 

 diatom, is rather that of accidental deformity, than that of definitive and 

 permanent character, and this view I was disposed to adopt, until after the 

 discovery of specimens altogether identical, from another and distant local- 

 ity. 



Like most of the Saco species, A. punctata enjoys a very extended range of 

 variation in size, length, proportion, definition of striation and punctulation ; in 

 no case, however, has the distinctive peculiarity (the unequally notched infla- 

 tion) been found absent. Indeed, bo invariable is it that a few worn 

 valves, in the mud, dredged from Wolfboro' inlet, (Lake Winnipisseogee), at 

 least sixty miles distant from the Saco pond, present this same special char- 



1863.] 



