ASCIDIA. 83 
of stigmata on each side of the branchial sac. Colonies of 
Leptoclinum, forming thin, white, grey, or yellow crusts, 
under stones at low water, are amongst the commonest of 
British Compound <Ascidians. 
Family IV. DreLosomip# :—Test reduced in amount, 
rarely containing spicules. Vas deferens not spirally 
coiled. In Diplosoma, the most important genus, the 
larva is gemmiparous. This is a common British form, 
especially on Zostera beds, and amongst sea-weeds. 
Family V. Ponycurnip# :—Ascidiozooids divided into 
three regions, thorax, abdomen, and post-abdomen. ‘Testes 
numerous; vas deferens not spirally coiled. The chief 
genera are—Pharyngodictyon, with stigmata absent or 
modified, one species: the only Compound Ascidian 
known from a depth of 1000 fathoms; Polyclinwm, with 
a smooth-walled stomach; Aplidiwm, with the stomach- 
wall longitudinally folded; and Amarouctwm,in which the 
Ascidiozooid has a long post-abdomen and a large atrial 
languet. ‘The last three genera contain many common 
British species. 
Family VI. Borryniui# :—Ascidiozooids having the 
intestine and reproductive organs alongside the branchial 
sac. Dorsal lamina present; internal longitudinal bars 
present in branchial sac. The chief genera are—Botryllus, 
with simple stellate systems, and Botrylloides,* with 
elongated or ramified systems. There are many species 
of both these genera, which form brilliantly coloured fleshy 
crusts under stones and on sea-weed at low tide. They are 
amongst the commonest and the most beautiful of British 
Ascidians. | 
* It is intended that a future L.M.B.C. Memoir will deal with Botryloides 
as a type of the Compound Ascidians. 
