49 



IX. — On the Structure of the Siliceous Loricce of the genus Arach- 

 noidiscus. By George Shadbolt, Esq. 



(Read November 14, 1849). 



The name Arachnoidiscus (appropriately chosen from the re- 

 semblance borne by the markings on these shells to the disposi- 

 tion of the filaments in a spider's web) was conferred on the genus 

 by Mr. Henry Deane, the first observer who discovered entire spe- 

 cimens of it. Single valves had, however, been previously met with 

 by Mr. Topping, Mr. Deane, and also by myself, amongst the 

 siliceous remains of infusorial animalcules from the Ichaboe guano, 

 but only very sparingly scattered. 



In a paper read by Mr. Deane, at one of the meetings of this So- 

 ciety, he mentions having met with entire specimens of the Arach- 

 noidiscus on some sea-weed from Japan, the sea-weed having been 

 prepared or preserved as an article of food ; and I understand he 

 has since met with them on another marine Alga from a different 

 locality. 



Mr. Marshall has, at least, one very beautiful species, which, I be- 

 lieve, he obtained from Professor Bailey, of New York ; and about 

 two years back I had given me, amongst other things, some Algre 

 brought by Mr. Moxhay from the Cape of Good Hope, having 

 attached to one of the specimens an immense number of individuals 

 of this genus ; hence it would appear that they are pretty generally 

 distributed about the globe, having been obtained from five different 

 localities lying so widely apart. The examination of these minute 

 organic bodies excites in the mind a high degree of interest, not 

 only from the exquisite beauty of the objects themselves, but also 

 from their relation to the fossil siliceous remains met with in all 

 parts of the world, sometimes in immense numbers, and in such infi- 

 nite variety of form. As some highly interesting and ingenious sug- 

 gestions have been promulgated respecting the former condition of 

 the strata, whence some of the fossil organic bodies have been ob- 

 tained, it appears to me, that the investigation of the structure of this 

 class of objects, whether fossil or recent, would tend to further the 



TRANS. MIC. S0C. VOL. III. H 



