106 PROCEEDINGS OF SOCIETIES. 



irregularly, divergent, more or leas interrupted, rays emanating 

 from a common centre — in a word, with a Cylindrocystis-like con- 

 figuration of the contents. But in the present gathering the 

 unconjugated examples showed the contents with a dense and 

 highly granular appearance ; it is, however, well known that at 

 times the characteristic arrangement of the contents in many 

 forms is so masked. The zygospore is very remarkable. It is cir- 

 cular, compressed (thus shaped like a round cushion) ; in the broad 

 view the margin is undulate, undulations nine to twelve, smooth ; 

 in the narrow (edge) view the zygospore is oblong-elliptic, sides 

 parallel and straight for a notable distance at the middle, then 

 gradually merging into the broadly rounded extremities, margin 

 smooth ; contents at maturity passing into a bright brownish- 

 yellow colour. An inspection of a zygospore in an oblique posi- 

 tion, or, still better, of an empty membrane, showed that the un- 

 dulations at the circumference of the broad aspect were carried 

 onwards over the front surface, and that the elevations converged 

 towards the centre, and at the same time diminished inwards, so 

 as to disappear ere they reached the centre, where the surface 

 appeared flat. The wall at the margins was considerably 

 thickened and colourless. Fresh examples of this curious zygo- 

 spore formed an extremely and unusually beautiful object. 



ISth October, 1877. 



Structure of Spiiie of Echinostrephus molare. — IMr. Mackintosh 

 exhibited cross sections of the spine oi Echinostrephus molare, 

 A. Agass., a genus belonging to the family Echinometridae. The 

 structure of the spines resembles in general plan that of Echino 

 metra, but differs in the much greater development of the solid 

 rays, which, expanding very rapidly, leave but little room for the 

 tubular tissue, which forms so conspicuous a feature in the spines 

 of Echinostrephus ; they, moreover, are very slender, the section 

 exhibited being only about -jL" in diameter. 



Structure of Scale of the Ganoid, Amia calva. — Mr. Mackintosh 

 also showed a scale of the ganoid Amia calva (kindly given to 

 him by Professor Macalister), and called attention to some pecu- 

 liar lacunae occurring in it. They were long, linear-lanceolate in 

 shape, and provided with a number of short, rapidly tapering 

 canaliculi, which came oif at right angles, and had no tendency to 

 anastomose. They were found grouped together towards the 

 centre of the scale immediately beneath the superficial layer of 

 ganoin. Scattered about through the rest of the scale were 

 numerous lacunae and canaliculi, like those of Lepidostem osseus, 

 a section of whose scale was shown for sake of contrast. 



JPlumularia echinulata, exhibited. — M r. Grant exhibited a speci- 

 men of Plumularia echinulata, Lamk., which had been taken 

 growing on Chorda fihim, between tide-marks near Monkstowu 

 Co. Dublin. This species, which is remarkable for the extremely 

 small size of the neraatopbores, occurs but sparingly on the 



