TRANSACTIONS OF SECTION C. 341 



these volcanic fragments, which are often coated with manganese, their association 

 with volcanic ash, and their lithological constitution, shows them not to he derived 

 from submarine flows of lava. They must rather be regarded as incoherent pro- 

 ducts — lapilli, the accumulations of which form in the Pacific a series of submarine 

 tuffs. 



One of the most remarkable facts elicited by the soundings in the Pacific is the 

 large share taken in these sedimentary deposits by palagonites, quite identical in 

 lithological characters with those of Sicily, Iceland, and the Galapagos Islands. 

 One may, in fact, call them glasses of the basic series, playing the most important 

 part among the sediments of the Pacific, and consisting either of sideromelane or 

 decomposed into a red resinoid substance. The small lapilli, of 2 or 3 millimetres 

 in diameter, are cemented by zeolites, the crystalline forms of which are those of 

 christianite. It is enough to indicate the presence of the easily alterable basic 

 glasses in order to show the source of the clayey matter with which they are 

 associated, since it is known that wherever rocks of this type occur there also 

 decomposition into clay is observable. 



Among the minerals present in the volcanic ash are rhombic tabular crystals of 

 plagioclase, augite, magnetite, with very little sanidine or hornblende. It is also 

 remarkable to notice that in these deep-sea deposits quartz-grains are practically 

 absent, in striking contrast to the coast deposits. It is not, however, this fact 

 which is most worthy the attention of the Section, since it is not so unexpected as 

 the formation of zeolites in the free state. The latter phenomenon takes place in 

 the zone in question, where fibrous radiated spherules are found in the mud, 0'5mm, 

 in diameter, and possessing the crystallographic character of christianite. Besides 

 these zeolotitic globules there are other crystals of the same kind in the form of 

 small prisms, not more than - 026mm. in length, and occurring in such prodigious 

 mimbers that they form about a third of the red clay. Orystallographically these 

 microlites must be referred to those forming the zeolotitic spherules. The authors 

 regard them as belonging to one species. The formation of these zeolites and of 

 the red clay in which they are developed is easily understood if one bears in mind 

 the lithological nature of the above-described basic tuffs and of their decomposition- 

 products. 



7. On Ammonites and Aptychi. By Charles Moore, F.G.S. 



The author remarked that ammonites and aptychi are always found associated to- 

 gether in beds of secondary age, the latter organism never being met with beyond 

 the range in time of that shell. The Aptycus is a peculiar triangular-looking body, 

 usually bilobed, oftenest found loose in beds containing ammonites ; but now and 

 then in the outer chamber which that animal occupied during life. In structure 

 it appears to be partly calcareous and partly corneous or horny. 



Probably no organism has given rise to so much speculation or to more diverse 

 views as to its zoological position. As far back as 1811 it was described as a bivalve 

 shell and named Trigonellites by Parkinson, since which time it has been raised to 

 the genera Munsteria and Aptychus, or considered by other authors as the plates of 

 fishes, valves of cirripedes, internal bony plates of Teudopsis, the gizzards of ammo- 

 nites, or a parasitic body attached thereto, and at last the general view arrived at 

 and still entertained is that they are the opercula of ammonites. 



The great variety of opinion thus entertained has arisen from the ammonite 

 having become extinct, its only living analogue being the nautilus, and even of this 

 genus only two or three examples with the animal have ever been obtained, one of 

 which was dissected and described by Professor Owen, the aptychus in the ammonite 

 being supposed to represent and to occupy the position of the fleshy hood in that 

 shell. 



In a paper published some years ago the author expressed a doubt as to the 

 aptychus being an operculum, one reason being that it was not of sufficient size to 

 cover the mouths of the shells in which they happened to be found, though for other 

 reasons he had no doubt they were allied. He had now obtained new facts, which 

 he would first give, and if he afterwards suggested any heterodox notion his justifi- 



