246 AMERICAN JOURNAL 



Tectura belongs to the restricted genus Acmoea, prevents the 

 use of that name for this group for which it might have been 

 advantageously employed. 



The miijonty of the Acma'ida' of the West American coast 

 belong to this section of the genus. 



Section A, ivitli one uncinus. {Typica.) 

 Type CoLLiSELLA PELTA, Esch. sp. Plate 14, fig. 6. 



Acnioea pelta, Esch. Rathke Zool. Atlas, V. p. 19, No. 5. 

 + (?) Acmcea cassis, Esch., ib. p. 19, No. 4, PI. 24, fig. 3. 

 = Patella Jimbriata, Gld., + leucopJio'a, Rvp. + montieola, 



Nutt. MSS. (pars.) + strigillata, Nutt. MSS. (pars.) fide 



Cpr. 



Soft parts : foot large, long, usually hiding the head when 

 viewed from below ; sides of foot smooth, blackish ; mantle rather 

 narrow, with a dark, broad, thick edge, furnished with a single 

 row of minute beards or filamentous papillae; head short and 

 broad ; tentacles stout, bluntly pointed, much swollen just above 

 the somewhat constricted base, with a large tubercle at the inner 

 base of each. Frill smooth, slightly crumpled, disk radiately 

 striate with a granular border ; mouth transverstly oval. Gill 

 short, acutely pointed with strongly marked borders, left margin 

 conspicuously crenate. Inferior lamellsB larger than the upper 

 ones, and the posterior laminge below much more produced than 

 the anterior ones. Anal papilla prominent, oblique, with a T- 

 shaped orifice, pointing to the right. Infra-anal do. smaller, 

 subcircular, deeply bifid. Renal orifice not elevated, situated 

 some distance to the left of the anal papilla. 



Liver small, linguiform. Radula short, forming a double loop 

 on the upper surface of the liver. Crop medium in size, not 

 laminated internally. Generative capsule divided by a deeply 

 impressed transverse sulcus, from below, into two lobes. Formula 







1^2 — LI — 2jl. Female examples had the sac full of ova in 

 different stages of development, but afforded no special evidences 

 of complexity of structure. On the other hand, the same organ 

 in the males was a gland, composed of innumerable small tubes 

 parallel with each other, perpendicular to the wall of the sac at 

 their bases, where they were thick and frequently bifurcated, 

 their internal extremity conical, pointed, and emptying into a 

 central, irregularly-shaped cavity. 



The whole structure recalled that of the kidney in vertebrates, 

 but was coarser. The tubes separated readily from one another, 

 were nearly smooth or lightly longitudinally striate ; their sheaths 



