MODIOLARIA. 127 



Yar. 2. semilcevis. Shell narrower, yellowish-horncolonr; ribs 

 on the posterior area slight and scarcely perceptible, L. 0*1 7-5. 

 B. 0-1. 



Habitat : Gregarious at the roots of seaweeds (espe- 

 cially Corallina officinalis) between tide-marks, and in 

 the Laminarian zone everywhere from Shetland to the 

 the Channel Isles. Var. 1. Southampton (J. G. J.) ; 

 estuary of the Orwell, Suffolk (Clarke). Var. 2. Staffa 

 (Alder). Some specimens from Lismore near Oban 

 also have no trace of ribs on the upper part of the pos- 

 terior area. Having had an opportunity of carefully 

 examining and comparing an extensive series of speci- 

 mens of Modiola laevigata, Gray, and the variety sub- 

 striata, from different parts of the Arctic seas, I am con- 

 vinced that they are not distinct from the present spe- 

 cies. The gradual passage from any one of these forms 

 to another is very evident, if a sufficient number ol 

 examples of all ages and from many localities are sub- 

 mitted to the inspection of a tolerably practised ob- 

 server; and the deplorable fashion of species-making 

 might be in some measure restrained by adopting this 

 method in all cases, instead of selecting a few particu- 

 lar specimens and discarding young shells and those 

 which offer inconvenient proofs of transition. As an 

 upper tertiary fossil the variety laevigata has been found 

 at Elie in Fifeshire by the Rev. Thomas Brown, and the 

 typical form occurs in the mammalian bed at Chilles- 

 ford. It has a wide extra- British range, from North 

 Greenland and New England to the iEgean. 



This little creature is a very industrious seamstress ; 

 for Mr. Alder says it " forms for itself a kind of nest or 

 case by stitching together the small seaweeds or coral- 

 lines with its byssal threads." Forbes and M 'Andrew 

 dredged it at a depth of 30 fathoms in the Irish Sea, off 



