191 



THE 



JOURNAL OF CONCHOLOGY. 



Vol. 13. JULY, 1911. No. 7. 



NOTE ON AN EARLY SPINOUS STAGE IN 

 CORBULA GIBBA (Olivi). 



By ANNE L. MASSY. 



(Read before the Society, March 8, 191 1). 



It does not seem to have been previously noticed that very young 

 examples of Corbula gibba have spines on the right valve at the 

 anterior side of the beak. A specimen measuring -5 mm. in length 

 and '75 mm. in breadth possesses three spines, graduated in size, 

 the one furthest from the beak being the largest. At this stage the 

 right valve scarcely exceeds the left in size. A specimen i mm. in 

 length and i'25 mm. in breadth has five spines in the same position. 

 These young specimens were obtained during investigations carried 

 out on board the fishery 'cruiser "Helga," of the Department of 

 Agriculture and Technical Instruction for Ireland, and were dredged 

 or taken in tow-nets attached to the trawl in the following hauls : — 

 November, 1904, 3 miles N. \ E. of Black Head, Co. Clare, sound- 

 ings i6| fathoms; May, 1905, 17^ miles S.W. \ W. of Coningbeg 

 Lightship, 40 fathoms; and February, 1906, 15 miles W.S.W. of 

 Chicken Rock, Calf of Man, 35 fathoms. Mr. Farran, who has 

 examined a series of these shells with me, is satisfied that they are 

 undoubtedly the fry of Corbula gibba. 



One of the above gatherings contained also a series of very young 

 specimens without spines and more or less of the adult shape. The 

 shells are much broader in proportion to the length in youth. 



With the above observation may be compared Professor Petersen's^ 

 suggested identification of Saxicava arctica with Saxicava riigosa on 

 the ground that in his experience all the specimens with longitudinal 

 ribs furnished with spines are small, and that the spinous ribs appear 

 to vanish with age. 



I Det videnskabelige Udbytte af Kanonbaaden "Hauchs" Togter. Copenhagen, 1889-93, 

 P- 93- 



M 



