GASTEROrODA SCUTIBSANCHIATA, 79 



Steomatia, Lam. 



The shell more hollow, the spire more salient, and the holes want- 

 ing ; otherwise resembling that of the Halyotides, which it thus con- 

 uects with certain species of Tnrbo. The animal is much less orna- 

 mented th n that of the H^ilyotides*. 



In the following genera, which arc separated from the Patella?, the 

 shell is perfectly symmetrical, as well as the position of the heart and 

 branchiae f . In the 



FiSSURELLA, Lain., 



We perceive a broad fleshy disk vuider the belly, as in the Patelhr, 

 a conical shell placed on the middle of the back, bvit not always 

 completely coA'ering it, and perforated at its sumaiit by a small ori- 

 fice, which affords at once an issue to the fa?ces and a passage to the 

 water, required for respiration; this orifice penetrates into the cavity 

 of the branchiae, situated on the fore part of the back, and in the 

 bottom of which terminates the anus; a cavity otherwise widely 

 opened above the head. A branchial coml^ is symmctric.iUy arranged 

 on each side ; the eyes are on the external base of the conical tcnta- 

 cula, and the sides of the foot are furnished with a range of fila- 

 ments |'. 



Emargixula, Lam. 



The structure of the EmarginuJse is similar to that of a Fissurclla, 

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

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

 which also penetrates to the branchial cavity ; the margin of the mantle 

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

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

 the margin of the foot is furnishes with a range of iilaments §. 



Parmophorus, Lam. 



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

 mantle, as in the Emarginulae ; the shell itself oblong, slightly conical, 

 and without hole or cmargination ; the branchise and other organs, as 

 iu the preceding genera |[. 



* IJalyotis imperforala, Gm., Chemn., X, clxvi, 1600, 1601. 



-J- They are the Paracephalora Cervico-braxchi^ Branchifera, Blainv. 



X All the Patellce of the fifth division of Gmelin, except Pat.fissura; among others, 

 Pal. grevca, List., 527, I, 2; — P. nimbosa, List., 52S, 4. \Ve have a species in 

 ■which the shell, at least six times the size of the mantle, simply surrounds the hole 

 of the summit like a ring, — Fissurella annulafa, Cuv. 



§ Patella fssura, L., List., 543, 2S, &c. The Palmaria, Montf., must be 

 allied to this genus. 



II Patella ambigua, Chemn., CXCll, 1918. 



N.B. FissureU(e, Emarginulce, and Parmaphon are also found fossil. 



