6 NEW-YORK FAUNA — MOLLUSCA. 



ORDER II. PTEROPODA. 



Body free, without arms or feet, but with two equal and opposite fins placed one on each side 

 of the mouth. Shell either present or entirely wanting ; when present, fragile, variable 

 inform. All marine. 



Obs. This order contains but few species, all small and hermaphrodite. The presence or 

 absence of a shell, with other modifications of structure, suggest a division into two distinct 

 families. I have not met with any representatives of the first family Hyalidce, on this coast. 



FAMILY CLIONIDM. 



Without any shell, but in its place a muscular covering. Head distinct ; no intermediate 

 lobe, but with one or several fleshy appendices in its stead. 



GENUS CLIO. Brug. 



Body oblong, sub-cylindrical, tapering, contractile. Head formed of two rounded tubes, from 

 which issue long retractile tentacula. Fins with a vascular net-work serving as gills. 



Clio borealis. 



PLATE I. FIG. 2. 



Clime. Pallas, Spicilegia Zool. p. 28, pi. 1. 



Clio borealis. Lin. Syst. Nat. Cut. Mollusques, p. ], pi. 1, figs. 1, 2. 



C. i<l. Lam. Am. sans vert^b. Vol. 6, p. 288. 



Description. Oblong, gelatinous, slightly compressed, tapering behind, truncated in front, 

 obscurely constricted in the middle. Head prominent, surrounded by retractile fibres, divided 

 by a furrow into two distinct tubercles, each pierced with a foramen, through which are pro- 

 truded three small tentacula. Fins two, opposed on each side of the neck, sub-triangular. 

 The excretory and generative ducts placed on the neck, under the fin of the right side. Two 

 small fleshy lips in front of the mouth. 



Color. Whitish transparent, occasionally tinged with reddish. 



Length, 0-5-0-9. 



This species occurs in almost incredible numbers in the Northern Atlantic, where it forms 

 the ordinary food of whales. It has been observed occasionally in great numbers in our 

 bays. In April, 1833, they weie very abundant, and of a blood-red color. After a few 

 days, they all disappeared. 



