Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 60 HALIOTIS.—FISSURELLA. ORDER OF GASTSROPODii SCUTIBRiVirCHIATA. 28. In the general form of their body and the position of their branchise, 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 approx
Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 60 HALIOTIS.—FISSURELLA. ORDER OF GASTSROPODii SCUTIBRiVirCHIATA. 28. In the general form of their body and the position of their branchise, 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 are not numerous, and are divided into Haliotis, Fis' surella.) <^c. 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 FissurellcB, \ {fig. 11) are recog- nised by their conical shell placed upon the ^ 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.
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