The Pen Shells. Sea Wings. Fin Shells 



set with erect, open, triangular scales. The horny shell sub- 

 stance is white and semi-transparent. Length, 6 to 8 inches. 



Habitat. — North Carolina to West Indies. 



The Black Pen Shell (P. nigra, Chemn.) spreads widely 

 from a narrow beak, and is constantly black. It rounds at the 

 lips. One specimen may be small and show a formidable array 

 of semi-tubular scales erect on the radiating ridges. Others, 

 remarkable for size, are smooth. Length, 6 to 1 5 inches. 



Habitat. — South Seas and Philippines. 



The Philippine Pen Shell {P. Philippinensis, Henley) 

 is a greatly elongated, narrow, straight-lipped Pinna with smooth, 

 pearly surface. Its colourless ground shows narrow smoky 

 streaks. Length, 8 to 12 inches. 



The Rough Pinna (P. rugosa, Sby.) is a strongly ribbed and 

 extravagantly tubercled species. The outline widens abruptly 

 from the narrow, stem-like umbonal region to the front, which 

 bears semi-tubular, leaf-like scales that twist very irregularly. 

 Colour, dark smoky. Length, 10 to 18 inches. 



Habitat. — In sand banks, Panama Bay. 



The Moor Pinna (P. Maura, Sby.), dark brown to black, 

 its posterior half covered with regular lines of similarly curving 

 tubular scales, is another handsome Panama species. Length, 

 6 to 8 inches. 



Oldroyd's Pen Shell (P. [Atrina] Oldroydii, Dall), a solitary 

 specimen, was taken up alive from a depth of twenty-five fathoms 

 by fishermen in San Pedro Bay. They brought it to Mr. and 

 Mrs. Oldroyd, of Long Beach, Cal., who recognised it as the 

 first member of its genus reported from this part of the world. 

 The remarkable "find" was nine inches long, and nearly black, 

 the lining gray with some iridescence. Dr. Dall published the 

 description of it in 1901. 



Cloth of Gold 



The anchor by which pen shells are held fast to rocks on the 

 sea bottom deserves special mention. More familiar to us is the 

 byssus of black threads by which mussels hang in clusters to 

 to bridge and wharf timbers below the water line. Pen shells 

 exude a gummy secretion through a sieve of much finer holes. 

 When exposed to the air this rope is found to be composed of 



A02 



