378 Reports and Proceedings — Royal Microscopical Society. 



YI. Braohiopoda. — The Bracbiopoda Lave their maximum 

 development in Palaeozoic times. Productus, Spirifer, Pentamerus, 

 Cyrtia, Merista, Uncites, and String a cephalus show not only great 

 abundance and extraordinary specialisation of forms, but also 

 remarkable variety of shape, size, and condition of their brachial 

 supports. They have a comparatively short range in time, both in 

 genera and species. 



The long-winged Spirifers, dominant in the Devonian, were 

 rapidly extinguished, but the simple Spirifer glabra ranges from 

 the Devonian into the Carboniferous. Any striking peculiarity of 

 growth or size seems to be followed by rapid extinction. 



In the Mesozoic period both genera and species are much reduced 

 in numbers, the forms chiefly belonging to the persistent Terebratula 

 and Bhynchonella types, with slight variations in their shell- 

 markings. 



With these are some exceptional forms, such as Lyra, Magas, 

 ^ingena, Trigonosemus, strictly Cretaceous; while a few others, as 

 Pygope, Dictyuthyris (specialised Terebratulce) , have a limited range 

 in the Jurassic period. From the Lower Palaeozoic period genera 

 like Lingula, Crania, and Discina have continued on, and are living 

 now. Such forms may be truly termed persistent types. In this 

 division hermaphroditism (so rare in this class) occurs. Lingula 

 shows great resistance to death, surviving after being out of water 

 and in a dry condition for some time. 



VII. Vermes (Worms). — Worms being all soft-bodied animals are 

 seldom found in a fossil state. Their former existence is, however, 

 proved by their tracks, burrows, and castings which they have left 

 in the sedimentary^ rocks /rom tlie Cambrian to tlie present day. Their 

 chitinous teeth and jaws have been exhibited by Dr. Hinde, F.R.S., 

 before this Society, and described and figured in the Quart. Journ. 

 Geol. Soc. London, 1879, 1880, and in the Transactions of the Royal 

 Swedish Academy. 



Many species construct tubes. These variously-formed cases- 

 (called Serpidce) are common in many formations, but do not disclose 

 much information about the structure of the animal itself. 



They admirably illustrate the persistence in time of very simple 

 and lowly organised forms, having bodies composed of a large 

 number of siaiilar segments (often capable of subdivision), and 

 possessing moreover great powers of reparation and reproduction 

 and resistance to death. 



VIII. MoLLUscA. — In the Mollusca, amongst the Lamelli- 

 branchiata, there are many persistent types showing very small 

 amount of variation. E.g., Solenomya has persisted since Carboni- 

 ferous times, and Nucida from the Silurian onwards. Both belong 

 to the ' Protobranchiata ' forms, with simple gills and a sole on the 

 foot for creeping upon — not a mere digging foot. In contrast to 

 these are the Rudistes, such as Diceras, Upper Jurassic ; Bequienia, 

 Monopleura, Caprina, Sph(srulites, and Hippurites, etc., from the 

 Cretaceous. These peculiar molluscs had a world-wide distribution, 

 and occur in such numbers that beds of limestone are often built up 



