APLIDIUM NUTANS. 29 



General mass about an inch (25 mm.) high and half 

 an inch (12 mm.) in diameter; individuals four lines 

 (8 mm.) long. 



Hah. Deep water. [Attached to under surface of 

 stones, sides of rocks, etc. (Cocks). ~\ 



ENGLAND. [? Cullercoats, Northumb. (Alder). Fal- 

 moutli, Cornwall (Codes). ~\ 



SCOTLAND. Berwick Bay, Berwickshire (Johnston}. 

 First record. Johnston, 1834. 



The individuals of this species are stated by Dr. 

 Johnston to be "nutant" or curved downward at the 

 top. This is probably only the case when the animals 

 are dead and contracted, as the apertures would no 

 doubt rise to the surface in a living state. Dr. John- 

 ston's figure of an individual agrees very well with 

 Savigny's second tribe of Aplidia : "Animaux filiformes, 

 a ovaire beaucoup plus long que le corps." We have 

 not been so fortunate as to meet with either this 

 species or Amaroucium fallax Johnst. ; our knowledge 

 of them therefore entirely depends upon Dr. John- 

 ston's descriptions and figures.* 



Genus 18. SIDNYUM Savigny, 1816. 



8idnyum SAVIGNY Mem. Anim. sans Vert. pt. 2 [1816], 

 p. 238. 



Colony turbinated, rounded above and contracted 

 below, sessile ; composed of several systems. Indi- 

 viduals elongated; branchial aperture 6-lobed ; atrial 

 simple, tubular, applied against the thorax. Thorax 

 and abdomen of nearly equal length, rather short. 

 Post-abdomen pedunculated, slender, dilated, and 

 filiform. 



By the above characters M. Savigny distinguishes a 

 genus founded upon a Compound Ascidian sent to him 

 from England by Dr. Leach. He considers it to be 



* [The figures (PI. LV, figs. 7-9) doubtfully referred to Aplidium nutans 

 were drawn by Alder from specimens found at Cullercoats. Under the 

 drawings, in his writing, is "Aplidium nutans, Johns. ? "j 



