MAZATLAN UNIVALVES 415 



spiraliter striatis, supra Icevibus ; aperturd ovali, peritremati 

 vix continue, plied sub distinct a. 



This species is known by the deeply cut channel above the 

 suture, and the transverse bars continued on the other side of 

 the channel in the form of fine lines running round to the 

 minute umbilicus, with the interstices minutely spirally striated. 

 The inner lip is seen best in dead specimens. The labrum is 

 indented by the channel. The number of transverse ribs is 

 variable. Long. '042, long. spir. '024, lat. '023, div. 25. 

 Hob. Mazatlan ; 7 sp. off Spondylus ; L'pool Col. 

 * Tablet 1964 contains the largest specimen. 



SECTION 33. Shell strong, short, spirally ribbed or nodulous* 

 500. PAETHENIA AEMATA, n. s. 



P. t. ovato-conicd, solidd, alia ; vertice nucleoso planato sub* 

 tumente, anfr. ii., subprominente, verticaliter sito, marginibus 

 spirce excurvatis vix super 'ante ; anfr. v. normalibus, quarum 

 prima lirulis transversis et cingulo basali, alterce seriebus 

 duabus spiralibus tuberculorum, et carinis duabus acutis in- 

 structce ; tuberculis maxime validis xv. xx., serie superiore 

 claviformibus, inferiore subquadratis, in adult a aperturam 

 versus compressis, pcene evanidis ; carind und majore in peri- 

 pherid, alterd in basin, parietem plicante ; plied columellari 

 inferiori ; aperturd ovatd ; labro tenui ; suturis impressis. 



This beautiful and highly sculptured species is somewhat 

 analogous to O. gemmulosa, C. S. Ad. Cont. Conch, no. 7, 

 p. 109, from Jamaica ; from which it differs in the number and 

 strength of the tuberculous ridges. The principal keel falls 

 into the suture of the succeeding whirl. The tubercles are not 

 parallel, being more numerous in the lower row. In the con- 

 traction of the lower whirl and thinness of the outer lip, it 

 resembles Chrysallida. Long. '1, long. spir. '076, lat. '034, 

 div. 28. 

 Hob. Mazatlan ; 12 sp. off Chama and Spondylus ; L'pool CoL 



Tablet 1965 contains the most perfect specimen. 



501. PARTHENIA EXAEATA, n. s. 



P. t. conicd, validd, parvd, albd ; vertice nucleoso minuto, in 

 parte truncatd celato ,- marginibus spirts subrectis ; anfr. iv. 

 profundississime exaratis, carinis iii. obtusioribus, validissimis 



