: ' u< ^- MODIOLARIA. 127 



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

 on the posterior area slight' and scarcely perceptible. L. 0-175. 

 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 

 jthe 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 lavigata, 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 of 

 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 l&vigata 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 JEgean. 



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 



