12 ACM^A. 



A. patina ESCH., Zool. Atlas, edit. Rathke., p. 19, t. 24, f. 7, 8. 

 MIDD., Sib. Reise, p. 187, t. 16, f. la-d, 2a-c, 3. CPR., Mazat. Cat. 

 p. 207 ; Araer. Journ. Conch, ii, p. 333. A. scutum ESCH., not 

 Orb. P. mammillata NUTT., Jay's Catal. no. 2839. RVE., Conch. 

 Icon f. 140. P. tessellata NUTT., Jay's Cat. no. 2885. P.fenestrata 

 NUTT., Rve. Conch. Icon. f. 121. P. verriculata RVE., I. c., f. 87 

 P. nuttalliana RVE., I c., f. 81. P. cumingii RVE., I. c., f. 37. Lot- 

 tia pintadina GOULD, U. S. Expl. Exped. t. 29, f. 455. Collisella 

 patina DALL, Amer. Journ. Conch, vi, p. 247, t. 14, f. 4 (dentition). 

 A. testiidinalis var. pato'na.DALL, Proc. U. S. Nat. Mus. i, p. 340. 



P. cinis Rv., considered a synonym of patina by Cpr., belongs to 

 A. pelta. P. strigillata Nutt. mss. is a form of fascicularis, judging 

 from the suite deposited by Nuttall in the Academy collection. 



This is the commonest of all western limpets. Although it has 

 been shown to intergrade with A. testudinalis on the Alaskan coast, 

 yet I cannot rank it as a variety of that species in the sense in 

 which alveus is a variety. It is thoroughly differentiated from testu- 

 dinalis throughout most of its range. The two forms vary in quite 

 diverse directions, patina having no form corresponding to the var. 

 alveus of testudinalis, but having its own peculiar mutations, not 

 found in the other species. 



It would be an advantage if we were to use the term " form " 

 (forma) for such mutations as alveus, nacelloides, etc., reserving the 

 rank of " variety " for true geographic subspecies. 



The principle mutations of A. patina are as follows: 



Var. PINTADINA Gld. (pi. 9, fig. 6). Large, flat, open, apex 

 subcentral ; tessellated white and dark. P. cumingii Rv. (pi. 42, 

 fig. 87) and tessellata Nutt. belong here as synonyms. This form 

 passes into the striped form nuttalliana Rve. (pi. 2, figs. 32, 33, and 

 also f. 36, 37). The last figures correspond to Reeve's verriculata. 



Another mutation is the form fenestrata Nutt. (pi. 9, figs. 10, 11, 

 12, 13, 14), of which cribraria Gld. mss. is a synonym. This shell 

 when young is dark olive closely dotted all over with white, the 

 eroded apex black ; when adult it is usually uniform dull slate-color 

 outside with a ring of light around the black apical spot ; inside it 

 has a wide dark border, a large, irregular central dark patch, and 

 generally is suffused with dark brown all over. Sculpture obsolete. 

 This form is from San Francisco, Santa Cruz, etc. 



Var. OCHRACEA Dall (pi. 9, figs. 7, 8, 9). Externally of a very 

 light yellowish-brown, without spots or rays ; internally white with 



