EMARGINULA.— PATELLA. 



61 



passage to the air necessary for respiration, and also for the ex- 

 pulsion of the excrements. 



31. We give the name of Emarginula to mollusks very much 

 like the Fissurellse, but their shell, in place of being open at the 

 top, presents a slit or notch in front, communicating with the 

 branchial cavity. 



OHBISH OF GiLSTEROPOD.A. CSTCI.OBKiiZrCIIIjA.TA. 



32. The cyclobranch gasteropods closely approximate the pre- 

 ceding, either in their general form, or in the disposition of their 

 internal organs ; but they are distinguished by their branchise 

 being fixed around the edges of the mantle [fig- 78). 



38. Some, the PatellcB 

 {fg. 78), for example, are 

 provided with a broad-based, 

 conical shell, which covers 

 the whole body ; they very 

 much resemble the Fissurel- 

 lee and Emarginulce, but the 

 shell is not perforated at the 

 apex, nor is there a notch in 

 front as in the latter. The 

 head is furnished with two 

 pointed tentacles, having the 

 eyes at their base, and a 

 stout trunk ; the anus is 

 situate to the right, and a 

 little above the head, and the 

 branchiae are composed of 



m-- 



Fig. 78. PATELLA. 



leaflets or fringes, arranged in a row around the body, under the 

 edges of the mantle. Patellae are found in almost all parts of the 

 world ; they are found on rocks to which they adhere, and lie 

 completely concealed beneath their shell, even after they are left 

 bv the ebbino; sea. 



Explanation of Fin 

 the edge of the shell 

 the head. 



78. — The animal of the patella seen from below; — c. 

 -p. the foot ; — m. the mantle ; — b. the branchiae : — t. 



3L How does the genus Emargi'nula differ from Fissure'lla? (Emargi- 

 nula, from the Latin, e, from, and margo, marginis, the margin — from 

 the margin — notched.) 



32. How are cy'clobranch ga'steropods distl'nguished ? (Cyclobranch, 

 from the Greek, kuklos, a wheel, and bragchia, gills.) 



33. What are the characters of the genus Pate'Ila ? (Patella, Latin, 

 knee-pan. 



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