136 AXEL A. OLSSON 



Subgenus LEIOSOLEJfUS Carpenter, 1856 



Type species by monotypy, Leiosolenus spatiosus Carpenter. 



Shell as in Lithophaga, s.s., but the surface covered with a thin, cal- 

 careous incrustation, not produced beyond the posterior end of the valves. 

 Burrow bullet-shaped, capacious, excavated in thick-shelled mollusks (Spon- 

 dylus, Chama) narrowly contracted towards a small orifice at the top and 

 often prolonged above the surface by a flattened, calcareous tube. 



This group was proposed by Carpenter largely on the character of the 

 burrow provided with an elevated, external accessory tube and noted that 

 if the animal, when examined, proved to have long, excurrent siphons, it 

 must take generic rank perhaps in the neighborhood of MytUimeria Conrad. 

 Elongated siphons seem, however, common to most species of Lithophaga. 

 The thin, fairly uniform encrustation covering the shell without posterior 

 appendages together with the elevated, bilobate accessory tube may be 

 accepted as characters distinguishing this subgenus. 



Lithophaga (Leiosolenus) spatiosa (Carpenter) Plate 15, figure 7 



Leiosolenus spatiosus Carpenter, 1856 (as a subgenus of Lithophaga) , Cat. Mazatlan 



Shells, Brit. Mus., pp. 178, 179. appendix, p. 550. (Mazatlan, in shells of 



Spondylus). 

 Lithophaga {Leisolenus) spatiosa (Carpenter), Soot-Ryen, 1955, Allan Hancock Pacific 



Expeditions, vol. 20, No. 1, p. 102, pi. 10, fig. 59. 

 Lithophaga abbotti Lowe, 1935, Trans. San Diego Soc. Nat. Hist., vol. 8, No. 6, p. 17, 



pi. 1, fig. 5 Kino Bay, Sonora. 



A specimen assumed to be this species was extracted from the lower 

 valve of a large Chama buddiana, which when detached from the rock on 

 which it was fixed, revealed the chamber of the Lithophaga with its shell 

 enclosed. The lower part of the lithophagid bore had penetrated the vol- 

 canic matrix on which the Chama was perched. The opening of the bore at 

 the surface of the chamid shell is relatively small and is continued into a 

 short accessory calcareous tube. There are several other of these small pipes 

 on the same Chama rising from 3.5 to 5 mm. above its surface. The litho- 

 phagid shell has a length of about 28 mm., thin, obliquely and broadly 

 elongated, the proportion of height to length about 1 to 2.7. The beaks are 

 small, almost terminal, the dorsal margin straight, then descending at the 

 posterior one-third to form a bluntly rounded end. The ventral margin is 

 slightly curved, narrowed somewhat at the obliquely rounded anterior end. 

 The valves are moderately convex, their surface covered completely by a 

 thin, calcareous coating but which does not extend beyond the posterior 

 end. Beneath the encrustation, the periostracum is brownish, molded over 

 the concentric lines of growth. Interior brilliantly pearly, the pallial and 

 adductor impressions showing but faintly. This shell measures as follows: 

 Length 28 mm., height 10.7 mm., diameter S.S mm. (right valve). 



The type of L. spatiosa has not been figured but there seems little 

 doubt that this identification is correct. The type of L. abbotti has a length 

 of 62.5 mm. which would indicate that this species may attain a large size. 



Range— GuU of California southward to Panama and possibly Ecuador. 

 Panama: Lagartillo near Las Tablas (boring into Chama buddiana). 



