BihUograjihical Notices. \:i^ 



sent good marks of distinction throughout the genus Echinus. The spines 

 are especially important, as from the examination of a single spine it is pos- 

 sible to pronounce on the species to which it belongs. To the geologist this 

 is evidently of gi-eat consequence, as frequently he meets only with a few 

 scattered spines. But when we leave the family Echlmdce, we leave this im- 

 portant character behind us. Among the Heart-Urchins the spines present 

 one common family structure. A single plate, either ambulacral or inter- 

 am bulacral, will also, from the arrangement of the spiniferous tubercles 

 which cover its surface, enable us to pronounce pretty certainly on the ani- 

 mal of which it formed a part. Thus, in this family of Echinodermata, from 

 an apparently insignificant fragment we can construct, as it were, a species, 

 even as the student of tlie Vertebrata, from a broken bone, can pronounce ou 

 the form and habits of the animal to which it belonged." 



To those — if such there be — who wandering on the beach, and no- 

 ticing a Sea- Urchin flung there by the retiring tide, view it merely 

 its part of the rejectamenta of the ocean — a thing to be glanced at 

 with contempt, and broken into fragments under the foot, we re- 

 commend the careful perusal of the following extract, and beg they 

 will treasure up in their " heart of hearts" the reflection with which 

 it concludes : — 



" In a moderate-sized Urchin I reckoned sixty-two rows of pores in each 

 of the ten avenues. Now, as there are three pairs of pores in each row, 

 their number multiplied by six, and again by ten, would give the great num- 

 ber of 3720 pores ; but as each sucker occupies a pair of pores, the number 

 of suckers would be half that amount, or 1860. The structure in the Egg- 

 Urchin is not less complicated in other parts. There are above 300 plates 

 of one kind, and nearly as many of another, all dove-tailing together with 

 the greatest nicety and regularity, bearing on their surfaces above 4000 

 spines, each spine perfect in itself, and of a complicated structure, and ha- 

 ving a free movement on its socket. Truly the skill of the Great Architect of 

 Nature is not less displayed in the construction of a Sea-Urchin than in the 

 building-up of a world !" 



Among the Echinida none are more attractive than the E. Uvidus, 

 a species which at the time Mr. Forbes wrote was believed to be pe- 

 culiar to Ireland among the British Isles, but which has recently been 

 discovered on the west coast of Scotland by the Rev. D. Landsbo- 

 rough. It is remarkable for its singular habit of boring principally 

 into limestone rocks, and living in the excavation thus formed. In 

 treating of this species the author gives the following interesting 

 particulars : — 



" Mr. W. Thompson informs me it is gregarious, and was seen abundantly 

 in rock pools at low water by himself and Mr. Ball when visiting the South 

 Isles of Arrau in 1834. It is always stationary, the hole in which it is found 

 being cup-like, yet fitting so as not to impede the spines. Every one lived 

 in a hole fitted to its own size, the little ones in Httle holes and the large 

 ones in large holes; and their purple spines and regular forms presented a 

 most beautifid appearance studding the bottoms of the gray limestone rocks' 

 pools." 



We now pass on to the Holothuriad.e, an order composed of ani- 

 mals much less known to naturalists in general than those of the pre- 

 ceding orders. " A Holothuria may be regarded in one light as a soft 

 Sea-Urchin, in another as a radiated animal aj>iiroxiraating to the 



