22 TESTACEA. 



animal and its shell, that the former, or a portion of it, remains constantly 

 exposed, because there is not sufficient room for its reception. The shell 

 may be so slight and weak where exposed, that it can afibrd very little 

 protection to what is weaker than itself ; or it may be entirely divested 

 of its external characters, and be deficient in induration of any avail, by 

 being imbedded in the flesh of the animal belonging to it. 



1. SIGARBTUS. Plate V., Figs. 1, 2, 3, 4, 5, 6, 7, 8. 



The preceding facts are exemplified in the Sigaretus, which seems 

 to be an animal interposed between the unguarded and protected, or 

 between the Limax and the Testacea. It certainly participates of their 

 nature, though it is not allowed to belong to either. 



Its form, proportions, and appearance, prove it a Limax, such as 

 distinguish the Testacea. 



This creature, like the Doris, when viewed from below, is seen to 

 consist of a head and a foot or sole. 



. Length of the body, from the tip of the tentacula to the posterior 

 extremity, an inch ; head distinct ; tentacula two, rather cylindrical ; a 

 large black eye at the external root of each. Both the shoulder and the 

 posterior extremity are rounded, and the whole body of the animal exact- 

 ly resembles a Limax. 



It is entirely covered by a thick somewhat fleshy cloak, very flexible, 

 and spreading considerably over the body. The back is quite convex, 

 the sole quite flat. The front of the cloak is extended at the will of the 

 animal, in a fold narrowly resembling the syphon of the Murex, the 

 Cypraea Europaea, and many similar tenants of shells. 



When the anterior of the cloak is not prolonged, or perhaps accord- 

 ing to the inclination of the animal, it is folded in such a manner, that 

 one of the eyes is always directed through the slit. 



The cloak is a covering similar to that of the Doris, and in crawling 

 both extremities of the animal extend beyond it. 



The Sigaretus swims supine. 



