GASTEROPODA SCUTIBRANCHIATA. 387 



Emarginula, Lam. 



The structure of the Emarginulae is similar to that of a Fissurella, 

 except that instead of the hole in the summit, there is a small cleft 

 or emargination in the anterior margin of their mantle and shell, 

 which also penetrates to the branchial cavity; the margin of the man- 

 tle envelopes and covers a great part of that of ihe shell; the eyes are 

 placed on a tubercle of the external base of the conical tentacula, and 

 the margin of the foot is furnished with a range of filaments(l). 



Parmophorus, Lam. 



A great portion of the shell curved by the reflected margin of the 

 mantle, as in the Emarginulse; the shell itself oblong, slightly coni- 

 cal, and vi^ithout hole or emargination; the branchiae and other or- 

 gans, as in the preceding genera(2). 



ORDER IX. 



CYCL0BRANCHIATA(3). 



The branchia3 of the Cyclobranchiata resemble small 1am- 

 ellsBj or little pyramids forming a cordon more or less com- 

 plete under the borders of the mantle^ very nearly as in the 

 Inferobranchiata, from which they are distinguished by the 



(1) Patella fissur a, L., List., 543, 28, &c. The Pai-makia, Montf., must be allied 

 to this genus. 



(2) Patella ambigua, Chemn., CXCIl, 1918. 



N.B. Fissurella;, Emarginula:, and Parmaphori are also found fossil. 



(3) M. de Blainville, who calls the order in which he places Doris CYCioBHAjr- 

 cHiATA, makes an order of the Patellee, and of the three preceding genera, which 

 he names Cehvicobhanchiata, whicli he divides into the Retifera and the Branchi- 

 fera. The Retifera are the Patellse, because he supposes that they respire through 

 the medium of a network in the cavity which is over their head. I have vainly 

 sought for it, however, nor could I discover there any other organ of respiration 

 tlian the cordon of lamellae which extends round the under part of the margin of 

 the mantle. See Anat. of the Patella in my Mem. on the MoUusca. 



