60 



HALIOTIS. FISSURELLA. 



ORDER OF GASTEROPODA SCUTIBHANCHIATA. 



28. In the general form of their body and the position of 

 their branchice, the scutibranch resemble the pectinibranch 

 gasteropods ; but they differ from the latter in their anatomical 

 and physiological characters. Their shell is very open, slightly 

 or not at all turbinated, and, like a shield, it covers the branchiae 

 or even the whole body. A peculiarity of their internal organi- 

 zation approximates them to the acephalous mollusks ; their heart 

 is traversed by the rectum and receives the blood by two auricles. 

 They aro not numerous, and are divided into Haliotis, Fis- 

 surella^ fyc. 



29. The Haliotides (fig. 76) have a slightly turbinated shell, 

 with a spire so small that it is only seen from the inside : it is 

 flattened and the aperture is very large. In the Haliotides 

 properly so called, there is along the columella a series of holes, 



through which the water reaches 

 a slit on the right side of the 

 mantle, and penetrates to the 

 branchial cavity ; the filiform ap- 

 pendages of the edge of the mantle 

 can be protruded through these 

 holes, and all around the foot there 



Fig. 76. HALIOTIS. 



is a double membrane cut in 



fringes and furnished with long filaments. On the outside of the 

 tentacles we find two cylindrical pedicles, bearing the eyes ; and 

 the mouth is armed with a trunk or proboscis. The external 

 surface of the shells of these mollusks are not remarkable ; but 

 internally they are covered by a layer of nacre, of the richest and 

 most beautifully iridescent colours. They are found in great num- 

 bers on the rocky shores of California. o 

 30. The Fissurella, \. 



(fig- 77 ) are rec .g- 

 nised by their conical 

 shell placed upon the m 

 middle of the back, and p 

 pierced at its summit 

 by a small opening 



which serves to give 



Fig. 77. FISSURELLA. 



Explanation of Fig. 77. p. the foot of the animal ; m. the mantle ; 0. 

 the opening at the apex of the shell, and the anus. 



28. What are the characters of the scuti'branch ga'steropods ? (Scuti- 

 branch, from the Latin, scutum, a shield, and branchiae, gills.) 



29. What are the characters of the Halio'tides ? (Haliotides, from the 

 Greek, als, the sea, and ous, ear ; sea-ear, or haliotis, and eidos, resemblance.) 



30. How is the genus Fissure'lla recognised ? XFissurella, Latin, Fis- 

 ura, a slit.) 



